“Nighfall” the wonderful short story? Seconded.
Nightfall the bloated carcass of the wonderful short story expanded to novel legnth by two authors who shoulda known better? I un-second it. 
But I’ll fourth Ender’s Game
Fenris
When Gravity Fails, by George Alec Effinger.
“Earth Abides” By George R. Stewart
Rendevous with Rama by Arthur C. Clarke.
Peyote Coyote has beat me to Joe Haldeman’s *The Forever War. Let me add his Worlds and Worlds Apart.
David Brin’s pretty far from cyberpunk, but I’d highly recommend Earth, the Uplift books (especially the superb Startide Rising, The Postman, and his current scifi/hardboiled P.I. combo book, Kiln People.
Uh, guys? I thought the OP was looking for “cyberpunk.” Maybe I hold to an overly narrow definition, but I don’t think that things like The Moon is a Harsh Mistress qualify.
My two favorite authors in that narrow genre are William F. GIbson and Bruce Sterling. The books I particularly recommend:
Gibson:
Novels -
Neuromancer
Count Zero
Mona Lisa Overdrive
Virtual Light
Idoru
Anthology of short stories-
Burning Chrome
Sterling:
Novels -
Islands in the Net
Distraction
Anthology -
Mirrorshades
They’re all sort of dated, but they have the “feel” you’re looking for. Also, a guy named Mel Odom (pseudonym, I’m sure) wrote a couple of things that weren’t very good, but were still fun.
Incidentally, Bruce Sterlings Artificial Kid is barely related to “cyberpunk,” but it’s very good.
Mockingbird by Walter Tevis.
“Walter Tevis is science fiction’s great neglected master, one of the definitive bridges between sf and literature. For those who know his work only through the movies, the lucid prose and literary vision of Mockingbird and The Man Who Fell to Earth will come as a revelation.”
–AL SARRANTONIO, Author of The Five Worlds saga
Samples .
Cyberpunk… ummm… don’t see anyone yet recommending Pat Cadigan… so I’ll recommend Pat Cadigan. (I liked Mindplayers, also Fools, set in the same milieu [though not always an easy read, that one]).
Eugene Byrne’s ThiGMOO is fun.
Alastair Reynolds (Revelation Space,Chasm City) falls somewhere between the “cyberpunk” and “hard SF” classifications. Worth a look, IMHO.
Hmmm… they feature things like bionic enhancements and artificial intelligences… Iain M. Banks’ “Culture” novels.
Tsk. Posted that, immediately remembered one I’d missed… Bruce Bethke’s Headcrash. Should be required reading, for A Certain Type of cyberpunk fan… very funny, for those who aren’t that Certain Type.
Caveat before reading: These are not Cyberpunk.
Since no one else has mentioned him, I highly recommend my all-time favourite sci-fi author, Olaf Stapledon. His books are often difficult to find, but they are well worth the search.
‘Last and First Men’ and ‘The Star-Maker’ are his two most famous and, in my opinion, truly mindblowing. The first reads almost like a textbook and the second somewhat so, although it has more of a narrative. The former is a history of the human race starting from the 1930s when the book was written and going millions upon millions of years into the future showing the next 20 or so steps in Human evolution (not all of them are steps forward either). The latter is a similar history… but of the ENTIRE UNIVERSE!
Both books show a lot of foresight into science fiction. Some of the story elements in them are among the first, if not the first of their subgenre. He deals with supercomputer-run distopias, virtual reality and more… all with a fascinating philosophy (he had a PhD in Philosophy) about the way the universe works.
A couple of other books of his worth noting are Odd John, about one boy who is one of the first of a more advanced human species, and Sirius, about a dog who is given above average human-level intelligence (it sounds somewhat comic but it is actually very depressing. He lives his life like a severely disabled person… possibly worse.)
Also, for short stories, in my book no one beats the comic sci-fi author Fredric Brown.