We play a gametype called "Glob Tag". You start out as a free for all. Once a player is "hit" they are fair game to get tagged in by any of the remaining players. It will come down to all VS 1 in the end and once he is out...the game is over. They're fast and fun games.
Alien is a great game, where one person is the alien, and everyone else is hunting him. The alien can only be killed if he is hit in the back, and, if they alien hits you, you have ten seconds to run away from your teammates before you become alien spawn, and have to assist the alien. You can still be eliminated normally (i.e. a hit to the foot). The alien's goal is to get everyone on his side, while everyone else's goal is to eliminate the alien.
Manhunt is also a great game, where one or two people are "The hunted" while everyone else are "The Posse". Posse tries to get the hunted, while the hunted try to eliminate the posse or evade them for a certain amount of time.
You could also try Pistol Whip, which is a game where everyone is armed with a spring pistol, and, when you tag someone, they turn to your team. After they are tagged onto your team, they can be eliminated by a second hit. It's sound lame, but it's kinda chaotic, and fast paced.
Assault is another good one, where the defending team, armed with spring shotguns and pistols, have to defend a zone from an assaulting team, armed with AEGs.
The drug deal is fun but requires a ref, and some dialog. You start with 2 teams each with an elected leader. The two teams will stand around the center of the field. The leaders will approach eachother with some form of case. One will be filled with paper or monopoly money(the money), the other will be filled with a couple sacks of bb's(the drugs). The leaders will converse. Then the ref will give a 1st wistle blow signaling the players to take cover, about 10 seconds later there will be a second wistle blow signaling the players to open fire. The team that either retrieves both cases and gets them to their spawn or eliminates the other team wins.