It doesn't get much simpler than this. A big figure-8 racetrack, with lots of baddies, and lots of stuff to kill 'em. (And your friends, of course.) All starting positions are in a row, so you could play this one as a real race... first one across the finish line wins. (Mario Andretti never had to worry about being shotgunned from behind...)

A pretty complicated map, but easy to get around. It's set up sort of in the shape of a lotus flower (hence the name), with big weapons available only inside small guardpost-like rooms with forcefields on the door. Lots of secrets, with teleporters to get you quickly to the hill, entire secret areas, and little touches everywhere. Great for team KOTH.

A space station with one large central room, and several outlying areas. Nice views from the hallways... and the staircase in the central room adds to the flow dynamics. (Not quite as effectively as it could, since the switch to raise and lower it is on the bottom level-if it were on top, you could trap people in the hole.) Big enough, and spread out enough, that two players might get bored.

Bungie's Duality, modified with Bobs that shoot grenades or lava globs. The idea is to give people without access to a network the challenge of a net game. (SPN stands for Single Player Network.) Works okay, except that bobs will never shoot like real people... and not much care was taken with the physics model. (Although the shots are right, the sounds aren't... sort of strange when you hear pistol shots,and turn around to see lava globs coming at you.)