So many. In terms of artistic achievement? Pushing musical boundaries? Sales? Creative influence? Personal preference? Consistent popularity? These categories tent to overlap, and it's very hard for me to go with just one.
But:
Death Cab For Cutie, Bloc Party, Kanye West, Broken Social Scene, Metric, the Arcade Fire, all for at least a few of the reasons listed above.
In terms of single artists, I'd say Kanye (totally changed the game and maintained consistent popularity) or Benjamin Gibbard (he's behind Death Cab AND the Postal Service, I mean come on).
Crusty VGchartz old timer who sporadically returns & posts. Let's debate nebulous shit and expand our perpectives. Or whatever.