Good thread, should be stickied so it doesn't get lost in the endless whine threads. Anyway....
Royal Rumble on top of a wind turbine
Stealing jets and helping other players with wanted levels
Breaking into the base and taking on tanks with an armoured car and stickies
Also racing round the base runways with friends dodging the military
Cargobob fun (well it was till it stopped spawning)
Waiting for a friends car to be delivered and then beating his mechanic with a bat
Get bounty, and then fly high over a road in a chopper and watch people go nuts looking for you. Bonus points if you use a cargobob and drop stuff on them (too late for me to do now )