|Hummer in action during a game|
1. Zombies. Zombies can be added into many gametypes in addition to being played with variations (Dismemberment, chopper, ect.) (Stampede chiming in here) Zombies are players who would normally be considered "out" but instead find a new life as a facilitator of game play, marching around the field and tagging players who are still alive. I like instituting this facet because it means people don't have to sit out during a game, and zombies help prevent standoffs/camping. The rules we usually play with this game are there is an OZ or two, and they start off unknown (like HvZ), tagging players. Getting hit with a dart means a 7-15 second stun for the player to get away. This can be altered as noted above with variations, including large ammo.
2. Catch 'em all/blob - best played with 6+ people, but not above about 15. (Everyone starts with unlimited lives, 15 second respawn. Free for all. When you get tagged, you respawn on that persons team. Play until everyone's on the same team).
3. Free for all - Make sure you set boundaries, otherwise, you'll get the one camper who'll come in mostly fresh on lives. Adding zombies helps with campers ;)
4. Freeze tag - getting hit with a dart/projectile/weapon results in the victim being frozen in place. A teammate may release/revive the tagged player with a touch to the frozen player's person (BE NICE. DON'T BE RUDE ABOUT REVIVING YOUR TEAMMATES.) Frozen players may be used as cover, with hilarious results.
5. Royal rumble
Royal rumble: Start off with one person in the field, with everyone else lined up on the sidelines. add a person every 15-30 seconds. One life. Go until there's noone left or keep cycling in the dead players 'til tired. Alternatively, you could try to enforce a lives system, where you have to get back in line every time you die.
Some gameplay video from a recent game he organized, taken by CrissWolfNerf.
Questions? Comments? Hopefully these game types or some variant will be useful to you!