I stumbled upon this site a few years ago, and was instantly hooked. As a sufferer of MOCD (musical obsessive compulsive disorder), this site was built for me. For awhile I was completely consumed with it. Addictive personality and such. Basically, Last.fm organizes your music by your play counts and tells you what you like the best. Songs, artists, albums, the last week, month, year. You find out a lot about your listening habits, and, if you're anything like me, you start trying to fuck with them.
And you can creep on other people, make "friends", see what their most listened to band is, catch someone listening to Miley Cyrus. And then you can judge them.
My top artists of all time were:
1) Florence + The Machine
2) Parov Stelar
4) Kings Of Leon
5) Kris Allen (he of American Idol fame)
6) Broadway soundtracks of all kinds ("Spring Awakening" and "Legally Blonde" were probably the biggest contributors.)
My top song was Florence + The Machine's "Howl".
I made a shiny new account match up with my blog back in March, and wiped my history clean. My stats reflect just this past year, and I'm kind of amused by them. They definitely reflect this year's pop/techno addiction.
My current top artists, for comparison's sake:
2) Alex Clare
3) Florence + The Machine
4) Miike Snow
7) Mumford & Sons
Current most played song is the Black Keys "Lonely Boy", and I cannot find a single video I can embed. Stupid licensing. Go here.
Check me out, and make your own!