What works in ArmA 2:
God Mode
Spawning Vehicles
Unlimited Ammo (Well, sort of. It will randomly do something similiar to setdammage 1 to you so you need God Mode on for this.)
Dropping the whole team from 5000m
Dropping bombs on every player's head. (This one is funny to see in the chat with 20+ "Blah was killed." messages.
Stripping everyone's weapons then giving them chopper miniguns (Sadly giving players tank guns dosen't work. Just makes the smoke and noise, and freaks the hell out of everyone around you. Still funny for that.)
Servers with signature verification are a problem though. There are ways around it, but I haven't investigated this. (Hook winsock and make the server think that you don't have the other unsigned stuff? Or just filter out the failure message and replace it with a success one before it gets to your computer.)