Bring a timer out and use it as a bomb, that's brought all sorts of fun into our games.
We've tried such things as:
Attackers having to push to a position and plant the bomb, then defend it until it detonates.
Defenders holding a bomb position until it detonates
Blackhawk down where one force starts in a vehicle and once engaged has to plant a bomb in the vehicle and hold it until detonation.
In all 3 game types the non-bombing force ends the game by disarming the bomb or removing it from the target zone. I love these for an end of the day wrap up as you can set the bomb timer to the time you have left and you know the game won't go over.