You can get them in Torrent and pirated VHS tapes, but Hulu is playing Mystery Science Theater 3000 online now. Only five full episodes—from seasons 4, 5, and 6—are available, however:

They got The Starfighters, Secret Agent Super Dragon, Monster A-Go-Go, The Rebel Set, and The Giant Gila Monster (which is great). None of those are my favorites, but I'd watch them again. In case you don't know what Mystery Science Theater is, watch this:

They do the same with cheesy movies—the worst they can find, la-la-lah—mostly science fiction. If you have never seen them, go check it out. If you are a fan, you are welcome. [Hulu—Thanks Bonnie]