Every now and again the clothing retailer Urban Outfitters releases music "soundtracks" available for download -- free of charge. They currently have 6 different albums available for download through iTunes, each containing around 26 songs. The soundtracks feature mainly Indie music, and bands you've never heard of... I've really liked a lot of the artists featured, and a lot of times they become pretty well known afterwards.
You can click here to download #6 (the most current album). There are links above on that page to download the previous albums.
Lots of free music is good and it's a great way to broaden your musical tastes! Give it a shot!