Dragon Ball Budokai series - obviously a great game to just get some Arcade fighting in, hopefully Sparking Zero is just as good!
League of Legends - Oh boy, how many hours I have spent!
Mario games in general, I think this one is self explanatory
(sorry to be more broad, but, Nintendo games in general are usually based around playing with others. I think one of the best examples is Wii Sports. The gimme of a game that everyone with a Wii had, hold some of the best time with friends.)
And who could forget Guitar Hero.... Who doesnt want to be apart of a band with the homies!