Knights of the Old Republic 1 and 2- Star Wars games that are pretty cool, though might be a little graphics intensive (3d graphics)
Uplink- a little out of the rpg mold, this is a game about hacking into various computers and companies and upgrading your equipment. Awesome soundtrack, imo.
Space Rangers 2- Kinda like Heroes of Might and Magic, but in space. I highly enjoyed this game, but it's not for everyone. Check out some reviews.
For turn-based strategy, you might look into such gems as
X-Com: UFO Defense and
Jagged Alliance 2.
If you're into adventure, check out
The Longest Journey and
Discworld Noir.
Emulation-wise (SNES), you might try
Chrono Trigger,
Lufia 2, and
Earthbound.
Actraiser,
Terranigma, and
EVO are a bit more action-oriented, but fun, nonetheless.
These were already mentioned, but I recommend them, too.
Anachronox- the first hour is kinda slow, but gets awesome later
Planescape: Torment- the most fantastic rpg I've ever played, but I'd only recommend this if you can appreciate literacy :P
Omikron: Nomad Soul- superb first half, but the immersion-factor gets a little muddled later on. Worth trying, at least.
Grandia 2- I really enjoyed this game, but some people swear the first one's better (I haven't played #1). The second one is available on PC, though.
Arcanum- one of the best rpgs in terms of role-playing. Your stats and conversation choices really DO make a difference (try playing a low int character and watch the language in your diary and conversations devolve into Cro-Magnon- hilarious!). Too bad its combat engine is kinda weak, though. Also, it was released in a semi-buggy state, so make sure to save often.
EDIT- If you decide to check out any of the old Bioware games (Baldur's Gate, Icewind Dale, Planescape: Torment), you might consider trying out this mod that allows you to play at unsupported resolutions (which is great because monitors/video cards nowadays are much more robust):
http://www.gibberlings3.net/widescreen/For Deus Ex (a neat old FPS, though it shows its age), there's a high-def re-texturing project in the works:
http://offtopicproductions.com/hdtp/For Knights of the Old Republic 2, a "total restoration" project that's (sort of) nearing completion:
http://www.team-gizka.org/index.html