An often-forgotten and misunderstood early Philip K. Dick novel is The Cosmic Puppets, first released in the late 1950s and reprinted over the years with covers that reflect publishers' (and the public's) changing perception of this weird book. First of all, as David Gill of Total Dick-Head points out, the novel is probably best viewed as fantasy — even though it's usually marketed as a book about "galactic invaders." The war may be galactic, he argues, but the "invaders" are from ancient Persia and they use magical weapons. Check out the strange ways the cover has been redone over the years, as the popularity of scifi versus fantasy has waxed and waned.
Obviously the late-50s cover is purely intended as scifi. The cover mentions a galactic invasion, and we see your classic mean invader guy with a lady in one of those This Island Earth-style containers.
Here is a later cover, which I'm guessing is probably from the 1980s, since it mentions Blade Runner on the cover (Dick didn't actually write a book called Blade Runner — that was the name of the film based on his novel Do Androids Dream of Electric Sheep). Probably this got issued in the wake of Blade Runner's popularity, and the cover clearly plays up the scifi angle, with giant men looking down FROM SPACE onto the small Virginia town where our hero discovers he's stumbled into another dimension (or is it?).
Interestingly, another 80s cover, from 1983, gives us a completely fantasy-looking scene. It's likely that this went into production before the popularity of Blade Runner brought Dick's work back into the public eye. For book-buyers, this would be the first time that The Cosmic Puppets would actually have a book cover that (somewhat) accurately reflects the fact that it's about a war between god-like creatures who use things like golems and enchanted insects as weapons. This guy kind of looks like Zeus rather than an "intergalactic invader." Of course, despite the fantasy themes, the book is still basically Dickish — our hero has come to his old hometown only to discover that it's gone and in its place is this magical alternate town where he actually died many years ago. So even though otherworldly creatures are battling it out, there's still that "who am I" and "am I really two people" thing going on.
Finally, there's the quality paperback version from the 2000s. Most of Dick's books have been repackaged by Vintage in a series that look roughly like this: large format, abstract cover, big computery-looking font. Also, note that we've swung back to a completely scifi-looking theme here. We even see a giant space scene in the background. I find this particularly interesting because by all accounts we are going through a fantasy novel renaissance, and many scifi publishers like Tor are selling fantasy titles as fast as scifi ones. So why not make this cover fantasy-ish to reflect the public's wish for more fantasy? Maybe because nobody wants to admit that Dick ever wrote about magic?
Covers and some back story via the awesome Total Dick-Head blog.