I found a good Unreal Tournament 2004 mod last weekend called Killing Floor. Inspired by the movie 28 Days Later, it’s a co-op mod where 1 or more players are deluged by 50 or more zombies at a time. You’ve also got to hunt for weapons, which makes things more difficult. You start off with just a knife, 9mm pistol, medical syringe, and a welder that can strategically weld doors shut. You have around 40 seconds to gather weapons and get in a defensible position before the zombies start attacking. It starts off slow but the zombies surround and overwhelm you before you realize it.
Very nice graphics, runs decently on my 2.4ghz Athlon with 1GB memory and GeForce 6800GT.
It comes with 4 or 5 maps set in an office, old manor house, city streets, and bio lab. You can get more maps here: DropCatch.com
I’ll say again that this mod is HARD. The zombies withstand a fair amount of damage. Go for headshots. You’ll have to learn the maps the the weapon spawn locations. However, if you want to cheat a bit, I had fun enabling a Mutator called Ballistic Weapons (RuneStorm Blog) It adds some very nice new weapons to UT2004, and it’s compatible with Killing Floor. You’ll be blowing the zombies away with shotguns, MP5s, Katanas, Rail Guns, and more. The only downside is you won’t get any more ammo for the weapons in the Killing Floor mod, so you’ll be down to your katana or knife at some point.