Seconding nerf war. The thing is you don't tell them you want a nerf gun fight. Excuse yourself from the room, and come back and if they face away from you, execute each one on the couch as fast as you can. If they face you when you return, strafe and keep on the move.
This is typically a bit more fair if there are other guns for them to eventually find and use. Think of your house as a deathmatch level and stock accordingly.
Board games are also a good one. Not your pansy ass monopoly and candy land, but something like Settlers of Catan, or anything with the name Reiner Kniza on it. If you need an ALL DAY distraction, Doom the board game or Decent (both by Fantasy Flight Games), are like the old heroquest games. One guy plays the monsters, everyone else plays guys trying not to die to monsters. You don't need a story, just kill, loot, next room.
