Sabotage:
At the beggining of a round, one member of each team is randomly selected to be the sabotuer. The rest of the team do not know who the sabotuer is on their team. The sabotuer's job is to try and stop his team from winning. However, the team must not know who the sabotuer is. This ussually results in clever tactics (ubers are so fun to waste

Domination:
A sub game that can be played between groups has developed based on this in game feature. In this the participating members are given the name of another player they have to dominate. When they have succesfully dominated a player they inform them they are the target and the player leaves the domination game after giving their nemesis the name of their target.
Various rules like screen shots and playing time have been added to prevent winning by not playing / avoiding other members.
The sub game continues until only one person is left standing.
I'm not sure how difficult it is to implement these sorts of things, but it has been done before on the VGN clan servers. Any ideas?