I think I'd probably have to say Hitchhiker's Guide to the Galaxy (hey, it's been a movie and a TV miniseries, even though fans generally seem to agree that those are two of the weaker versions of the story). Futurama is pretty far up there as well. Of course, neither of these would have existed if there hadn't been "serious" science fiction to spoof.
I do want to see the new Star Trek film. bethje and I might go this weekend, after she's finished with her exam. I haven't actually seen all of the other Trek films yet. I know I've seen 2, 3, 4, 6, Generations, and First Contact. I think I might have seen 5 as well, because I remember Kirk, Spock, and McCoy singing "Row, Row, Row Your Boat."