Forgot to add a couple to my previous list:

DarkStar One was entertaining for a short amount of time.. wasn't exactly Freelancer but was entertaining nonetheless.

Star Wars: Knights of the Old Republic (first and second) both were great RPG's that could be completed in a day or two and you don't even have to be a Star Wars fan to enjoy them. Not alot of PC gamers played them because the console versions came out months before the PC versions, just like Fable: The Lost Chapters.

also The Suffering a neat FPS/horror title that takes place in a freakish prison and is more intense than it is scary.

Don't forget Godfather.. very few people I know actually played this one through but I enjoyed it alot. Apparently Dead Space's brilliant display uses Godfather's game engine.

Some great lists.. Anyone remember Sam & Max Hit the Road or Day of the Tentacle? Actually I think they were pretty popular back then but great slapstick comedy games that this generation might never have played (a little buggy on XP/Vista without a windows 95 or DOS loader)

Did you all play Soldier of Fortune II Double Helix? The single player had an intricate story line that suddenly went crazy but somehow dragged me through it.. judging by the number of multiplayer servers there were I don't think it was too popular. Kingpin was pretty sweet for a generic shooter with gang aspects to it... especially because I got into Max Payne shortly afterwards.

Savage was a pretty neat idea, an RTS + FPS. I was a huge fan of Natural Selection (halflife mod) at the time and Savage as a full game seemed like a neat departure but hardly anyone played it.

Rise of Nations was my favorite game for a long time (and it's expansion Thrones and Patriots aka RoNTaP) but again, it was difficult to find players to play with about a year after it came out. Also played ALOT of the original Red Alert and Shogun: Total War because the idea just seemed awesome, things were simpler back then. Emperor: Battle for Dune was one of the first RTS games with a fully 3D-engine and the benefit of Westwood's awesome FMV sequences with a great story told in the background.

Evil Genius or Dungeon Keeper 2 .. both fun games where you get to play the bad guy, controls can be a bit quirky and difficulty tends to scale quite quickly if you don't build your bases in a certain way.

Games that have already been listed that I also recommend:
Chronicles of Riddick (found in a used game bin and had awesome graphics almost Doom 3 quality)
Vampire the Masquerade: Bloodlines (too bad Troika went under, one of my fav half-life 2 engine games)
FreeSpace 2 (holy crap - did the build up toward the last few levels feel worth playing or what)
Freedom Fighters (im not very patriotic but this game really made you identify with your character)
Deus Ex (take system shock 2, take out the horror story, add more robots, and give more stat points)
NoX (I played Diablo 2 until I got sick of it then got into great game)
Freelancer (great game, small modding community, client-side multiplayer handles = cheating big problem)

so many others... and if you haven't tried it yet, go play World of Goo!