I prefer the C&C Series. It just doesnt get any better than throwing a weather storm, sending in a harrier fleet, and chronospering in a bunch of prism tanks directly into the unsuspecting enemy base all at once. Then pressing the HAHAHAHA taunt key while your online foe watches his base crumble.
Starcraft is cool too. When I was a n00b, for ranking I would play as zerg and bury a bunch of lurkers into my allies bases for "protection". Then, when we have almost killed our enemies, I un-ally with all of them, and after two seconds you see 10 messages seeing "WTF?!" as their base is trampled to smithereens. I just laugh when they send all their air stuff at me and I unbury all the enhanced hydralysks from under the ground and squash them.
Dirt tactics.
At a LAN place here in memphis I tried to pull that on a bunch of asian/korean people playing the game. When they saw their base go to peices, they freaked out! good times, good times.