I could recommend Decker. Not sure if it qualifies as an RPG, though.

I thought of one:
Rise of the Dragon.
Very good but ancient adventure game that is very, very cyberpunk. The annoying this about it is the Sega CD version has full voice and the DOS one only text. Not sure if Sega CD ROMS exist, but that might be the way to play the game.
The DOS version is abandonware and can be found for free legally.

Discovered a fairly recent cyberpunk-themed game: Neuro Hunter (2005). It is supposed to be a budget title ($6 on Gamer's Gate, DRM-free), but I'm having a blast playing it at the moment. Unfortunately, we get caves instead of slums, graphics are rather poor, and the menu beep will soon get on your nerves, but other than that, it sure gets lots of things right.
I think I'll post a more detailed review on GOG after I play it enough.