For PC, that would be Runescape way back in middle school. Me and my friends played that pretty obsessively... then we realized it wasn't really a great game and stopped.
For consoles, definitely Warhawk. I played that game a ton, and while I've been obsessed with Resistance 2's co-op, I always seem to go back to Warhawk every once in a while. Maybe it's because I met most of my PSN friends on there!








