Brute Force is great 4 person multi-player game on one TV. Brute Force is also a great single player game as well. Four people can play in Campaign mode, Deathmatch and Squad Deathmatch(each person controls 4 characters, for a total of 16 characters running around the map!). The cool thing about Brute Force, is that another player can join in at anytime, even in the middle of a mission, totally cool.
Dead or Alive 3 is one of the best fighters out there and it has a great 4 player tag-team mode. The trash talking and laughs will get intense during 4 player tag-team mode.
Phantasy Star Online also supports 4 player split screen on one TV. Multi-player PSO kinda has a Gauntlet feel to it, but with more RPG elements. You also MUST HAVE Xbox Live in order to play PSO offline, which kinda sucks. If you have XB Live though, PSO is great fun.
Also keep an eye out for Dungeons and Dragons Heros by Atari, for the Xbox later this summer. I'm not sure if it will be a 4 player dungeon crawler, like Gauntlet, or limited to two players like Baulder's Gate: Dark Alliance.