Campbell-award-winning sf author Jay Lake has challenged readers of his blog to come up with sf high-concept mashups, along the lines of "A Canticle for Lebowski" —
*Repo Man from UNCLE–Emilio Estevez is recruited for a shady job that turns out to be working for an undercover spy network that has developed a flying car/time machine.
*A Boy and His Dogma: A young archangel rescues the mother of God from a gang of roving ex-angels and attempts to conform to her human expectations. Rated R for the grisly ending where Alanis Morissette and Alan Rickman… well, I won't give it away.
*The Hitchhiker's Guide To The Galaxy Quest – Dent Arthur Dent discovers that all of his adventures were scripted episodes from an old TV show, the Heart of Gold is actually a 14" plastic model lit with Christmas lights, the Vogons are just big lumps of latex with Warwick Davis pulling levers inside, and Alan Rickman actually went insane holding up both ends of a conversation between Dr. Lazarus and Marvin the Paranoid Android.
(Thanks, Danjite!)