Here are some cool user-created changes:


Rocket Race

Players form teams of two with one VIP. The VIP cannot drive and must be escorted to each checkpoint before the other teams. Everyone has a rocket launcher, but the only way to die is to assassinate someone.

Rocket Race
Valhalla Rocket Race map
Sandtrap Rocket Race map


Ninja Pit

A variant on King of the Hill. All players have an energy sword. Outside of the hill, they are invisible, and agile. Inside the ring, players become visible and slower.

Ninja Pit (I couldn't find a direct link. It should be the fourth one down.)


Zero-G Rockets

Gravity is set as low as possible. Speed is bumped up to 150%. Ammo is infinite. Hilarity ensues.

Zero-G Rockets


Joust

Meant to be played with two-person teams, Joust has players riding on Mongooses with energy swords and gravity hammers. Definitely a fun activity for those of us who enjoyed crashing Warthogs into each other in Halo 1.

Joust
Valhalla Joust map


Laserball

Everybody has 300% Speed and 50% Gravity. All players start out with a Spartan Laser with infinite ammo. There are no weapons on the map, but grenades restock themselves. As soon as someone picks up the ball a ton of lasers appear. First to 250 points wins.

Laserball


Paintball

Players start with battle rifles. Maps variants are filled with crates and cover. Simple and fun.

Paintball
Sandtrap Paintball map variant


This is only part 1.....