You've probably heard of eMusic, the online store that sells DRM-free MP3s. If not, well, it's an online store that sells DRM-free MP3s. The service traditionally offers 25 or even 50 free downloads as part of its one-month subscription trial, but right now you can get a whopping 100 tunes absolutely gratis.
eMusic boasts a library of 3.5 million tunes, the bulk of them from indie artists like Sufjan Stevens and Belle and Sebastian, but also a fair share from mainstream names like The Raconteurs, Barenaked Ladies, and Taylor Swift. The service now offers audiobooks as well. Needless to say, because the downloads are unprotected MP3s, they'll play on anything: iPod, Zune, Zen, Sansa, BlackBerry, PC, etc.
The trial has no strings attached; if you cancel within 30 days, you walk away with your 100 free songs. But I urge you to consider becoming a subscriber, which you can do for as little as $9.99 (good for 30 downloads per month, the equivalent of 33 cents per track). eMusic is a fantastic service (see my dated but still mostly accurate review) that's well worth the money if you're into music.