Fully patched UT3 with Titan pack. Can also extent it with extra custom maps.
Would also suggest trying out The Haunted mod (Winner of Make something Unreal). Polished 4 player coop or play against each other (one teams summons and pocess the monsters)
eish, we haven't been able to play LAN for a long time :-(
but we used to have moesa lotta fun with Blood2 back in the day, and its still fun! http://www.the-chosen.com/ http://en.wikipedia.org/wiki/Blood_2
its a bit old now, but it so different from many of today's FPS shooters... so still great fun. ( i luv the voodoo doll and that 'screamer stick with the scull on"... "aaaaaarh")