I downloaded a new app for my iPod Touch called Top 100's by Year by Bing. The app streams the "top 100" songs from each year from 1947 to 2010, one year at a time. The app information describes the tunes as, "songs that have stood the test of time" so they aren't necessarily the most popular songs of the years. Although the songs play on a shuffle mode, you can skip ones that you don't want to hear.
I'm not sure I would have paid for it since I don't generally buy apps for my iPod, but it's worth a free download. It's completely entertaining to listen to songs from a particular year. But I wonder who ranked the songs on the lists? Is Free Bird really the top song of 1973?