Perfect Dark Zero, Call of Duty 2, Call of Duty 3, Far Cry Instincts Predator and Tom Clancy's Ghost Recon Advanced Warfighter - all of them support local 4 players multi, but are old 2005/2006 games. You can even play Halo 2 on your 360. I know it is even more old, but it is still fun to play. If you are big Goldeneye fan you can try Perfect Dark Zero.
About Halo 3 and Call of Duty 4 - yep they are new and better games, but I'm not 100% sure that both of them support 4 players local and I'm not sure that playing them more then 2 persons on one TV is a good idea. If you can find another 360+TV you can play on System Link (Up to 18 players for Halo 3)
I found that the best game for 4 players on one TV is Dead or Alive 4, but it is not a FPS. Versus Tag Teams mode is real fun.







