We play a bunch of fighting ROMs as well...those are fun at 4 am.

Total Anihillation is always fun, As for dog fighting try X-Wing V Tie Fighter.

Uhm... Quake 3? Is that 7 years old yet?

If not, UT2000.

Edit: On second thought, forget about Quake 3.  Just go for UT2000 no matter what.  It's a better game

Baldur's Gate. I think it's close to 10 years old now(1998 - 2001 for the entire series), but it's still got fanmodding being done for it, so once you add on a couple of expansion packs, and gameplay, item and class tweaks, you can have a completely new experience.
BG1tutu(play the original BG game using the BG2 engine and rules) alone is something I'd love to get a lan party together for, cause it's hard to get it to work on a full internet multiplayer mode, but it's fine for Lan play.

oh wait, missed rule #3. It's not freeware, but it has really shallow copy protection, so you can do a full install on all of the computers and just burn a couple copies of the main CD that lets you play the game.

Hrmm... this seems more of a quick pickup style games though. Baldur's gate is a D&D game so it requires more time commitment to really be able to enjoy. i think it took me close to a week to play through it completely on my own.

I never found RPGs to be the creme of a LAN party. You need super competitive games like UT2004 and RTSes. The best part of a Lan party is being able to yell at the guy across from you about how much he sucks. I myself have never had any experience with dogfighting games, but then again I have only stuck with FPSes, RTSes, and fighting games.