The cyberpunk movement in science fiction, like anything worthwhile with punk in its name, had already pretty much run its course by the time it became trendy. In its latest form, it was always less a proper literary movement than a set of stylistic tics and choice of subjects shared by William Gibson, Bruce Sterling, and a few close collaborators; many of the great writers in what would later be called the cyberpunk ouvre wrote before the term had even been coined.
Alfred Bester originated many of the stylistic choices that would later be considered cyberpunk in the 1950s: the explosive but hard-as-nails prose, the slick, angry antihero, the whole style-over-substance deal. He even wrote a short story, The Fifteen Minute Fugue, which was set in a grim, stratified and megacorporate-dominated East coast-spanning megalopolis.
In the 1970s, Phillip K. Dick and, to a lesser extent, John Brunner laid even more of the foundations. Brunner wrote The Shockwave Rider, a prescient look at the role that computers have in organizing a hypercomplex society like ours, which is probably more relavent now than the day it was written. But, of course, though this was some of the substance of what was to come, we've already established that style over substance is our mantra.
For the immediate genesis of the style of cyberpunk, we don't really need to look much further than one man, Phillip K. Dick. Of course, most roads in recent science fiction (really, of recent fiction in general) lead back to Dick by one way or another, but here the path is most direct. Dick was the master of paranoia, of writing about drugs and craziness and everything just not making sense anymore. He could evoke a world which had just become so fucked that there was no rational way of dealing with it anymore better than anybody. And this is what the cyberpunk authors would all try to do in one way or another.
What changed everything was this guy, William Gibson, writing this book, Neuromancer, which was so damn good that nobody could ignore it. He was already collaborating with the Mirrorshades Group, a smallish group of like-minded young writers, but after Neuromancer broke the big time, everybody wanted in on the action. Some of these writers which followed him were good, both within the little cabal (e.g., Bruce Sterling), and without (e.g., Walter Jon Williams). Many, many more were derivative and terrible. One, Neal Stephenson, deserves credit for picking up the ball and moving with it into a new territory entirely.
But cyberpunk, as a sub-genre, is more or less moribund now, a victim of its own success. The whole movement quickly became stereotyped, and each new trashy paperback or role playing sourcebook with a day-glo picture on the cover of an angry man with sunglasses and coax jack in his forehead was another nail in the coffin. Even Gibson has since moved into new territories, which are only still considered cyberpunk because he's the one who wrote them.
The next New Big Thing still lurks, half visible, just off the horizon.