A lot has changed in the digital-music industry over the past few years.

These days, online downloads account for 20% of music sales and are expected to overtake sales of compact discs by 2012, according to a recent report by Forrester Research ( FORR).

Digital music has gone legit. It's been embraced by the music industry at large, and loads of companies from record labels to phone companies are jockeying for a cut of the billions being spent on digital music every year.

Apple's ( AAPL) iTunes store has become the standard bearer for (legal) online music retailers, with some analysts estimating the company's market share at 85%. But the proliferation of other online music stores and rising competition from Microsoft ( MSFT) to Verizon ( VZ) has begun to threaten Apple's dominance.

For starters, major record labels, including Universal Music Group ( UMG), Sony Music Entertainment ( SME), Warner Music Group ( WMG) and EMI, have in the past year been busy signing deals with music sellers such as Best Buy ( BBY)-owned Napster, Amazon.com ( AMZN) and Rhapsody. As a result, digital-music retailers have full access to the major labels' immense music catalogues.

Here's a rundown on the companies aiming for a slice of the fast-growing digital-music industry and why consumers might start looking beyond iTunes.

Zune is Microsoft's digital-music software. In addition to organizing your music and videos, the software offers access to Zune Marketplace, an online music store much like Apple's iTunes Store. For $14.99 a month, you can sign up for a Zune Pass, which allows you unlimited downloads. You can listen to those downloads for as long as you hold a Zune Pass subscription, but you can choose 10 tunes a month to add to your permanent music library. The Zune store is engineered to work with Microsoft's Zune MP3 player, which holds up to 30,000 songs and can be synced to your Zune's software.

Verizon and Rhapsody, an online digital music retailer with more than 6 million songs in its library, have teamed up to allow Verizon customers to download music from Rhapsody straight to their cell phones. The Rhapsody subscription costs $14.99 a month, which allows you to download unlimited music onto your PC, which you can then transfer to up to three PCs or mobile devices. One caveat: You can't burn those songs on a CD because each track contains Digital Rights Management encryption. If you want DRM-free tunes, simply pony up $1.99 a tune to download to your phone, or purchase songs at the Rhapsody store for $0.99 and manually transfer them to your phone.

Amazon.com's MP3 store offers 6 million songs through major-label deals with BMG, Universal, Warner Music Group and EMI. Songs are priced at $0.79, $0.89 and $0.99, making recent or popular songs a better buy at the Amazon MP3 store than at the iTunes Music Store, which charges a top price of $1.29 for the most popular downloads.

Though its name at one time was synonymous with "copyright piracy," Napster is one of the best places to download music legally. Users can tap into its library of 6 million songs at $0.99 a pop, or pay a monthly subscription fee of $9.99 for unlimited free downloads. The catch is if you use the subscription service, downloads are essentially tethered to your computer. If you want to be able to transfer music files on to an MP3 player or burn them on to a CD, you will need to pay for the $14.95-a-month premium service. And watch out for the fine print: Once you cancel your subscription, the music files no longer work.

Harper Willis graduated from the Gallatin School of Individualized Studies at New York University with a concentration in ancient theater and jazz guitar. He is a musician and writer, and lives in Brooklyn, N.Y.

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