Here are suggestions from various LAN parties I've thrown with my friends:
* Unreal Tournament (Original) - Released in 1999, it surprisingly runs flawlessly on every system I've tried it on. Worst case, you can run software rendering and get a real blast from the past. Most machines should now be able to run this at Thousands of Frames Per Second. There is no frame lock.
* Wolfenstein: Enemy Territory - Free
- A team based axis vs. allies world war 2 game, this was one of the first to have mission objectives, like CoD. Find it here: http://www.splashdamage.com/content/wolfenstein-enemy-territory-barracks
* Starcraft - Many of us already have this, but if we stick to Original, we could work out Spawn installs for multiplayer.
* Warcraft III - Many fun custom maps
* Age of Empires 2 - Classic. Compatible. "Start the Game Already!"
* Total Annihilation - Crazy old fun RTS. Balanced? Not so much. http://www.gog.com/game/total_anihilation_commander_pack
Doomsday - a fun open source doom engine mod to play DooM with. Includes modern features.
As I find more, I'll add them to the list.