DRM-free music stores ideal for PSP use
To try it out for free, check out this week's free MP3, Ripe from Ben Lee. One of the great things about downloading music directly to your PSP is that it includes the album art for the song -- a nice touch that we can appreciate.
Another service you may want to consider is the Zune Marketplace, which recently added the largest collection of DRM-free music to its library. However, that requires downloading the Zune program, and connecting your PSP to your PC and transferring files manually.