I think it remains to be seen what band will define the "00s" ("aughts"? the "nothing" decade? Cripes, I'm glad it's almost over, even though "the Teens" doesn't sound any better, LOL). I'm thinking "hit the scene between 2000 and 2010" and nobody sticks out, really.
I can't speak with much authority, because I have no idea who's selling the most product or has the most fans right now, but I'll bet it will turn out to be a "pop" group or performer, as opposed to a "rock" act. Just one of those decades... it happens. Doesn't mean the decade was not "happening"; the #1 single or album does not a decade make, really.
There was a lot of amazing and very popular music (pop, rock, jazz, soul, doo-wop) out there in 1953, for example, but the #1 hit in the USA was a syrupy version of a song from the late 1800s!! It has more to do with the way music was marketed back then than with what people were listening to, but still... that ditty sold more records in the US that year than any other recorded single. Based on this alone, one might assume that half of the 50s was nothing but insipid fluff, music-wise.
Yes, I'm talking about:
http://www.youtube.com/watch?v=2AkLE4X-bbU&feature=fvw
It was supplanted in 1954 by "Rock Around the Clock" by Bill Haley and the Comets... who, for many people, defined the "50s sound". Definitely one of my favorites from that era!
http://www.youtube.com/watch?v=Ud_JZcC0tHI