It's the ultimate loss - the destruction of your entire planet, and science fiction is full of characters who have had to live through this unimaginable tragedy. Warning! At least one truly massive spoiler ahead...
But first, let's lay down the ground rules as to what I would call the "destruction" of one's planet:
I. If the character's planet explodes, that definitely counts.
II. If the planet in question is rendered instantly uninhabitable (due to, say, nuclear war), that probably counts, assuming the character (and any other survivors) had to then find a new planet on which to live.
III. If the planet's destruction was more gradual (like due to environmental collapse) and there was time to evacuate most of the planet, I'm not going to count that, if only because there's nothing particularly special about the character's survivor status. However...
IV. If the character in question is the only survivor, then whatever the circumstances of the planet's demise, I'm counting that.
With all that in mind, here's the list...
1-11. Superman (and every other alien in DC Comics)
Obviously, Superman is pretty much the originator of this archetype in modern science fiction, what with him being the Last Son of Krypton. That said, the last few years in comics have seen the (re)introductions of a fully Kryptonian Supergirl, a "third Kryptonian" who survived Krypton's brief foray in interstellar warfare, General Zod, Ursa, Lon, a whole gaggle of Phantom Zone criminals, Christopher Kent, and most recently 100,000 Kryptonians released from Brainiac's imprisonment. So for someone who for so long was defined by his cosmic uniqueness, the Man of Steel is now part of a very, very big crowd.
Superman is far from alone in the DC Universe when it comes to surviving the death of his home planet. The Martian Manhunter is one of only a tiny handful of his people, the Green Martians, to survive the destruction of Mars (although there are significantly more of their brother species, the White Martians). Admittedly, J'onn J'onzz is somewhat dead at the moment, but after Superman he's the most iconic survivor of a dead world in all of comic books.
You might also want to count Superboy-Prime and Power Girl as separate cases from the other Kryptonians, as they were first the only survivors of Krypton in their respective universe before the Crisis on Infinite Earths (well, Power Girl also had the Superman of Earth-2, but work with me here) and are now the only survivors of their entire universes, not to mention two of the only people who trace their origins back to the original, infinite multiverse.
The Legion of Superheroes members Element Lad and Blok are the only living members of their respective races, while Kilowog, the lovable Green Lantern with a fondness for calling people "Poozers", is the only survivor of Bolovax Vik. There's also the planet another Green Lantern, John Stewart, accidentally blew up back in Cosmic Odyssey. The destruction of Xanshi turned one of its princesses, who was being educated off-world at the time, into the villain Fatality.
Teen Titans stalwart Starfire was next in line to rule the planet Tamaran before it imploded in a war with the Psions. Recent events also saw the destruction of Throneworld, the home of the other other other Starman, Prince Gavyn, at the hands of Lady Styx. Oh, and then there's always Lobo, last of the Czarnians, who exists pretty much to parody all the other examples on this list, as he blew up his own planet on a whim.
Clearly, the creative types at DC have a thing for blowing up planets, but there at least a few other examples of this in the rest of science fiction. Let's take a look at those now.
12-14. Arthur Dent and company from The Hitchhiker's Guide to the Galaxy
Saved from the Vogon constructor fleet's demolition of Earth by the alien travel writer Ford Prefect, Arthur Dent lacks a lot of the internal angst and survivor guilt of most of the people on this list, probably because he's just so easily befuddled. Along with Trillian, a beautiful young woman Arthur was doing a halfway decent job of flirting with before Zaphod Beeblebrox, the only slightly insane President of the Galaxy, whisked her away, he is now one of the only two Earthlings left in the entire universe.
Well, at least until the Magaratheans finish building another one or before he spends a decade stuck in prehistoric Earth with a bunch of hairdressers or until the dolphins do whatever it is they did in So Long and Thanks for All the Fish to restore the planet. But then the Vogons finally finish the jobs through the multiverse (or the whole sort of general mishmash, as Douglas Adams preferred to call it) in Mostly Harmless, finally and completely destroying the Earth, taking Arthur and Trillian along with it. But Eoin Colfer's upcoming continuation of the saga, And Another Thing, will likely resurrect them in some capacity, as otherwise it would be a pretty uneventful book.
Though he never appears in the books themselves, one might also count Ford Prefect's father, who was the only person to survive the mysterious Great Collapsing Hrung Disaster of Gal./Sid./Year 03758, which probably destroyed the planet of Betelgeuse Seven, although Ford's father was always rather hazy on the details.
15-19. Spock (and at least a couple other aliens from Star Trek)
One of less than 10,000 survivors of Nero's destruction of the planet Vulcan in the new Star Trek movie (told you there was a massive spoiler in here), Spock might now be the most famous example of this particular trope. I'd also wager Spock is going to be pretty much the only Vulcan seen in future movies, what with the older, Leonard Nimoy version of Spock keeping all the other survivors busy rebuilding their civilization on New Vulcan.
You can't mention the new Spock without also acknowledging Nero and the crew of the Narada are the only survivors of Romulus. Well, then again, all their time traveling left them dead and the fate of Romulus in the new timeline is now uncertain, so maybe they only count in the original timeline.
There's also Guinan from The Next Generation, who had survived the destruction of her planet El-Auria at the hand of the Borg. There are also a lot of planets, particularly in The Original Series, that seemed to have a single inhabitant (mostly of the godly or energy being variety), but I won't count those as the planets themselves seemed mostly unaffected.
OK, I'll make an exception for Bele and Lokai from the legendary episode "Let That Be Your Last Battlefield", in which the consuming racial hatred of their two peoples (one's skin is black on the left and white on the right, while the other is black on the right and white on the left) has left those two the last survivors of a war that has destroyed their planet Cheron. Admittedly, they don't survive for very long, not when there's an opportunity to finally kill each other.
20-26. The Doctor from Doctor Who (and maybe a couple others)
Spock isn't the only famous alien to get the Superman treatment in recent years; Russell T. Davies and company blew up Gallifrey before the new Star Trek movie was still in the earliest planning stages. Actually, between the Doctor and Spock both losing their planets in recent revivals of their series, you'd maybe think there's some sort of trend in modern science fiction that finds lone aliens more interesting than entire alien cultures. And I'm not sure they're entirely wrong.
Anyway, The Doctor is one of the most angst-ridden survivors you could imagine, which I suppose is understandable considered he kind of was the one responsible for destroying Gallifrey. Of course, it also turned out The Master survived (at least for a little bit, pending an inevitable resurrection) by running away to the end of the universe, and there are ever so slightly more credible than usual rumors that the Rani will return in the next series played by Gillian Anderson. But either way, the Doctor is for now the Last of the Time Lords, and he'll be the first one to tell you that. (No, seriously - he really could tone down how much he mentions that, as it's kind of a downer.)
Still, the Doctor wasn't the first person to occupy the TARDIS who had survived the destruction of an entire people. That tragic distinction goes to Nyssa, who watched her planet Traken be destroyed by the bizarrely universe-spanning threat in Logopolis. To her credit, she's much more stoic about this than the Doctor, although that might have been because the show's writers never really bothered to come up with a cohesive character for her.
Gallifrey also isn't the only planet the Doctor blew up, as he quite decisively destroyed the Dalek homeworld of Skaro back in the unspeakably awesome seventh Doctor story Remembrance of the Daleks. Although new series Daleks like the one in Dalek or Dalek Sec might plausibly claim to be "the last of the Daleks", probably the best candidate to call a "survivor" of Skaro's destruction is the lone black Dalek at the end of Remembrance, left all alone in the entire universe after the destruction of all his comrades on Earth and the rest of his race back on Skaro. Of course, the Doctor then uses the overwhelming despair of fact to literally talk him to death, but for a good five minutes there he was indisputably the Last of the Daleks, at least until they came back. Again. And again. And again...
The classic City of Death, written by Douglas Adams, introduced Scaroth, last of the Jaggaroth. Four billion years ago, he and a few other last refugees of his warlike race fled the destruction of his planet and came to primordial Earth. He then proceeded to accidentally kill of the rest of his race when his spaceship exploded. The decidedly less class The Hand of Fear showed Eldrad, a genocidal outcast of his silicon-based race, who had survived the extinction of his species by being encased in rock for 150 million years (well, that is one way to do it). And let's not forget The Cybermen - the original versions, anyway - who survived the destruction of their planet Mondas in The Tenth Planet and became the marauding terrors of the galaxy (or, if not exactly terrors, then certainly minor annoyances, depending on how well the particular story was written).
27. Princess Leia
The full impact of this gets lost in the shuffle of all the action in the original Star Wars, but Princess Leia is forced to watch her entire planet be destroyed, leaving her quite possibly the only survivor of Alderaan in the entire universe. (Well, there are probably a few diplomats on Coruscant and elsewhere, but the movies don't give any evidence to support this. The Expanded Universe says there were about 60,000 Alderaanians off-world at the time of its destruction.) Admittedly, she's technically not from Alderaan at all, as she was born in space to a mother from Naboo and a father from Tatooine, but she spent all but the first twelve or so hours of her life as the daughter of the Organas, rulers of Alderaan, so there's no way she doesn't count.
Also, Princess Leia is probably the best example of the kind of cognitive dissonance Douglas Adams talked about when he described Arthur Dent's reaction to losing his planet - it's too big a tragedy to really comprehend, and thus impossible to properly grieve. Leia never really seems to deal with her Alderaan's destruction, although I suppose she could have worked through her emotions during the year or so between the events of Star Wars and The Empire Strikes Back. Honestly, it's sort of weird how Alderaan is just completely forgotten in the later movies. You might think "Remember Alderaan!" would be an effective battle cry for a rebellion trying to remind people of the Empire's monstrous crimes. Bit of a lost marketing opportunity there. But I digress.
28-29. The Survivors of the Twelve Colonies and the Final Five on Battlestar Galactica
OK, it might be a bit of a stretch to count the Galactica and the rest of the fleet as quite the same thing as the others on this list. After all, none of the Twelve Colonies were exactly destroyed, but the Cylon-launched nuclear bombardment did make then uninhabitable to humans in very short order (and thus my reasons for Rule II become obvious). Sure, Helo, Anders, and a bunch of other survivors managed to live on the charred remains of Caprica for a few months, but it was clear they had no long-term future on that world, even if they did manage to escape the Cylons indefinitely. Perhaps a stronger case can be made for The Final Five, who used an orbiting satellite outfitted with their recently rediscovered resurrection technology to survive the destruction of Cylon Earth some 2000 years before the events of the series.
30. Cale Tucker and the rest of humanity from Titan A.E.
And finally, we have this somewhat forgotten 2000 animated film (co-written by Joss Whedon!), which considers the fate of humanity in the year 3028. The race of energy beings known as the Drej have destroyed Earth in retaliation for whatever the humans discovered in the mysterious Project Titan. The survivors are now nomads who are generally ignored or looked down upon by the rest of the galaxy. Ultimately, Cale Tucker, the son of one of the scientists responsible for Project Titan, helps lead humanity back from the brink of extinction and comes up with a plan to create a new Earth. I mean, of course he does - after all, he's voiced by Matt Damon, and that guy can do anything.
In any event, that's more than enough to get this list started. Who else is out there in science fiction nursing the unimaginable pain and survivor's guilt of being the last of one's kind and without a planet to call one's own?