[gurgeh]

-Catch-22 (I know it's been mentioned several times, I just think this should be your next read).

-If you like Heinlein you should take a look at Frank Herbert (Dune) and Iain M. Banks. The latter wrote my favorite book of all time, Use of Weapons. Also see Excession if you like the play between ship minds, or The Player of Games for obvious reasons.

-H.P. Lovecraft if you like horror (mostly short stories, so you won't get stuck in a novel you don't like).

-Sir Arthur Conan Doyle if you like mystery (see above comment).

-Anything by Kurt Vonnegut. Slaughterhouse Five is his most well known book, but all the other novels I've read have been similarly satirical, humorous, and insightful. Hocus Pocus comes to mind specifically.