CJ: The best OLD sci-fi book I ever read was a classic. War of the Worlds, by H.G. Wells. It's frightening in it's authenticity. The world it's set in...WW1 esque Britain, is awesome, but the characters are what drive it.
I loved the musical as well. It gave a whole new dimension to it.
Post-Apocalyptic Playground: It is a sci-fi book that I have shamefully never read, although (completely unrelated to this segment) The Mothership located an old copy within their dwelling the other day so now I have no excuses! Likewise though, it's the musical which always stays with me (rather than the Tom Cruise/Spielberg vehicle) and I can even hear the music as I type!