This is the official list of games that got the most demand via our forums. These titles are going to get the most attention, so if you're thinking about picking up some for the LAN, now is the time. Please have them installed and updated before the LAN. Remember: This list is not intended to restrict any gameplay; if you have a title you want to play, by all means you're welcome to get a game going. This list is meant to help for planning and preparation.
StarCraft 2
Team Fortress 2
Counter-Strike: Source
Lead and Gold: Gangs of the Wild West
Trackmania Nations Forever
Diablo 2: Lord of Destruction
Demigod
Alien Swarm
FlatOut2
Dirt 2
Day of Defeat: Source
Worms
League of Legends
Unreal Tournament '99/2004
Call of Duty 4: Modern Warfare
Call of Duty: Modern Warfare 2
Battlefield: Bad Company 2
Crysis Wars
Peggle
More information can be found
here