Apple is celebrating "A Decade of iTunes" with a cool interactive timeline in the iTunes store. The timeline pulls out milestones for iTunes each year. For example, on September 7th, 2005 it says "iPod nano replaces iPod mini and goes on to become the bestselling music player ever."
Each year also displays the the Top Ten bestselling singles and albums. The entire timeline is actually really cool -- especially if you're an Apple history buff. There's no way to grab a direct link to it, but to see it just open up iTunes, go into the iTunes store and look for the "A Decade of iTunes" white carousel banner at the top.