I know you all have the select games that drain away your life slowly, but there are a few (demos, mostly, mind you) that could be pretty kickass to set up a server and play in. Noteably:
Rainbow Six 3 - i had the demo a bit before the game was out, and it was awesome playing online, the demo has multiplayer and would be awesome.
Alien Vs. Predetor (2 is the best) - again, same as Rainbow Six (most of these are like Rainbow Six, so i won't be explaining them).
Battlefield 1942 - Same gameplay as Battlefield 2, without the need for a fantastic computer.
Postal 2 - Heh.
Savage: Battle for Newearth - Part third person hack-slasher-ish. Part strategy. Kickass.
Soldier of Fortune 2
XIII - Really, really cool game to play online. The style is great.
All those are just demos, but there is one or two full-free games.
Wolfenstein: Enemy Territory - I've been playing this longer than UT, and i still love it. One of the best online games out there.
Quake 3 Arena - I think this is freeware? If not, then not this.
I mentioned demos so none of you would have to go out and buy them, and they're still fun to play. They also all can run on less-than-stellar computers.
www.fileshack.com <where i got 'em all.
Just trying to expand your horizons.