For me, no one else compares to Rise Against.

I suppose for me, it all comes down to personal taste. They're a great rock band, and I haven't really listened to a whole lot of this decade's music. But they have so many great songs. They're one of the few bands I can say is truly great today, especially after the steps Green Day took with American Idiot. My second favorite would probably be Rammstein. Oh, and the band/music artist shouldn't be a band with re-released songs like The Beatles (as much as I love them).

Seriously, Rise Against is just amazing. Listen to this:

Okay, enough of that. Post your own!

Postal Service.

Oasis

Rise Against, I guess.

Lupe Fiasco!

Outkast

Kristin Chenoweth, no contest

I'm going to have to go with Metric:

Levon Helm

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).

Radiohead were my favorite of the decade.