So you just bought a new MP3 player, copied your entire CD library onto it ? and it's still only half full. The immense storage capability of modern portable music players allows users to indiscriminately indulge themselves with thousands of songs, books, and other audio files. But where do you legally get all of this content? And with so many download services out there, which one is right for you?

We've done the legwork for you and compiled information about the cost, compatibility, and content offerings of seven of the most popular (and legal!) music download services: AOL Music Now, Audible.com, eMusic, Napster, Rhapsody, Urge, and Yahoo!.

Happy downloads.

Note: The iTunes Music Store, Apple Computer's digital content download service, is not included in this list because content downloaded in iTunes can only be transferred to an iPod.

AOL Music Now

With a library of more than 2 million songs and the backing of one of the most recognized names on the Internet, AOL Music Now is a web-based download service that allows users to stream or download music instantly. The service has music from all major labels, so odds are if you hear the song on the radio, you can download it from AOL. The service also gives users free access to thousands of radio stations specializing in a variety of musical genres. Songs that are downloaded can be accessed and copied to a portable device for as long as the membership is still valid. Files come in WMA format, making the service not compatible with iPods, but it does work with any PlaysForSure device.

Memberships cost $9.95 per month, and include unlimited access and downloads.

Audible.com

Unlike all of the other services, which offer music downloads, all the content on Audible.com is spoken word. The site contains more than 27,000 files for download, ranging from books, radio shows, newspapers and magazines to informational and educational programming. Audible.com is the iTunes Music Store's exclusive supplier of all spoken word content, and downloads are compatible with all portable devices, including iPods. Once files have been downloaded, they can be burned to CD, transferred to other computers, or added to as many portable devices as desired; you own the content.

There are three different levels of subscription available from Audible: AudibleListener, AudibleListener Gold, and AudibleListener Platinum. Memberships are not required in order to download, but the prices are significantly lower for members than non-members. Each subscription level comes with a different number of download credits that can be used to purchase content from the site. Nearly all items on the site can be downloaded for one credit, including books, and subscriptions to radio shows.

• AudibleListener
  The AudibleListener membership costs $9.95 a year and provides access to members-only sales and other promotions. No download credits are included with this plan.

• AudibleListener Gold
  The AudibleListener Gold subscription costs $14.95 per month ($149.50 per year) and provides one download credit per month. Up to six of these credits can be "rolled over" to the next month if not used, and one free download credit comes with the membership.

• AudibleListener Platinum
  For $22.95 per month ($229.50 per year), users can opt for the AudibleListener Platinum subscription, which includes credits for two downloads per month. Up to twelve unused monthly credits can be "rolled over" to the following month, and new subscribers receive one free download credit.

Sample Genres: Mystery, self-development, fiction, nonfiction, business, comedy, horror, young adults, romance, and classics

eMusic

eMusic has more than 1 million songs from over 3,800 record labels to choose from, making it the favorite among independent-music enthusiasts. Users can choose from established and up-and-coming artists in each genre, or receive song recommendations from respected music industry columnists. It is the only major music service to offer all of its content in MP3 format, meaning that the music plays on all digital media players including iPods. Since all of the songs are from independent labels, they are not subject to the digital rights management that accompanies content from major record labels. This means once songs have been downloaded, they can be burned, copied, emailed or otherwise used at the owner's discretion.

Customers are given a choice of three subscription levels (Basic, Plus, and Premium), each of which allows a certain number of song downloads per month. Songs cannot be downloaded on an individual basis. Subscriptions are available on a monthly basis, and can be cancelled at any time.

• Basic
  The Basic subscription offers 40 downloads per month for $9.99

• Plus
  The Plus subscription offers 65 downloads per month for $14.99

• Premium
  The Premium subscription offers 90 downloads per month for $19.99

Sample Bands: Bloc Party, the Drive-By Truckers, Gomez, Interpol, Belle & Sebastian, Tom Waits, Nick Cave, Pedro the Lion, Dolorean, Calexico, Arcade Fire, Spoon, Dar Williams, Ron Sexsmith, Modern Skirts, and Ryan Adams