eMusic offers downloads of MP3s via monthly subscription. Since the files are MP3, they are not protected and are widely compatible with computer-based methods of playback and on portable players like the iPod.
eMusic covers a very wide range of labels but doesn't include the big five music labels probably because they don't distribute unprotected content. Examples of some the moderately well-known labels available on eMusic are Fantasy (Credence Clearwater Revival) and Fat Possum Records (blues and modern blues-rock bands).
One purchases a monthly subscription to download a number of songs. There are no roll-over songs, which can become frustrating for the user that likes to download complete albums. For example if the user has 3 songs left for the month, he has to find another album, download 3 songs, and then remember to download the rest of the songs next month. Of course one can purchase extra songs in a month for a premium.