Based on scrobbles:
1. Lady Gaga - 18,487,195
2. The Killers - 12,471,57
3. Lily Allen - 10,522,633
4. The Prodigy - 8,900,264
5. Franz Ferdinand - 8,795,186
6. Beyonce - 8,642,704
7. Animal Collective - 7,630,636
8. Green Day - 7,607,693
9. YEAH YEAH YEAHS - 6,885,404
10. KANYE WEST - 6,615,339
HONORABLE MENTIONS:
11. Britney Spears - 6,268,504
12. Fall Out Boy - 5,954,548
13. Taylor Swift - 5,512,011
15. Black Eyed Peas - 5,280,181
17. Paramore - 5,066,577
18. Kelly Clarkson - 4,943,886
I thought LAST.FM is full of POP retards like us in ATRL but I'm wrong.