Sort of extending from the comments on the Solaris post, a brief non-expert introduction to Polish science fiction author, Stanislaw Lem. Lem is an author who is not afraid to dig into difficult concepts and push them all the way to their farthest possibilities. He's a hard science guy, but often with a wicked (or sometimes silly) sense of humor. I've read fourteen of his many books (and somehow never managed to read Solaris), and they seem to fit into three rough groups:
1) Hard science, nuts and bolts problem solving.
2) Amusing fables for the future.
3) Heady, no-holds-barred philosphical/cosmological thought experiments.
My starter picks in each category:
1) Tales Of Pirx The Pilot, His Master's Voice
2) The Cyberiad, The Star Diaries
3) A Perfect Vacuum, Imaginary Magnitudes
If you want to pick one for fun, go with The Cyberiad -- fairy tales for robots, sort of. Finally, here's a brief and rather bleak (but typically blunt) interview from 1996.