Last week I discovered The Hype Machine, a daily music blog aggregator. Subscribe to their RSS feed in a podcatcher like iTunes and you'll never have to buy new music again...but you might have to buy a new hard drive to hold all the mp3s you're downloading.
In 7 days, I've received 1031 songs, 5.5 Gigabytes of free music through this aggregator. The music ranges all over the board -- from the Monkees to Public Enemy. There's truly something there to suit everyone's fancy...the only problem is deleting the stuff you don't like to save disk space!