CNET'S QUICK GUIDE: Online music store guide

Online sales may be a small piece of total music sold in this country, but they're growing at a swift rate. After the sudden success of Apple's iTunes Music Store, other companies rushed to launch their own stores, determined to get a piece of the digital pie. It's an ever-changing space: each time a new store pops up, another one (see: Sony Connect, Yahoo Music Unlimited, and so on) bites the dust. It might seem late in the game for new entries, especially given the death of some of the larger competitors, but the space continues to grow and diversify, offering specialty content and community features. Choosy music buyers should consider the many options available before settling on one--or several.

We've put together this guide to help you sort through the a la carte music store options, though we also touch upon the subscription aspect of certain music services. a la carte refers to a store where you pay per track or per album, then own that album, whereas most subscription services essentially rent out tracks for your listening pleasure. (As a subscriber, you also have the option to buy individual tracks outright, sometimes at a discounted rate.) Some subscription services even let you take this rented music to go on approved portable devices. For the complete lowdown on this type of music service, see our guide to on-the-go music subscription services.

Although most stores are in the midst of switching to all DRM-free MP3 catalogs, some sell music in a format that is only compatible with a particular player. Your first step in choosing a store should be determining which stores are compatible with your portable music player, since online music stores won't give refunds if you find you've made a mistake later on. The general rule to keep in mind is that (most) songs purchased from iTunes play only on the iPod, while songs purchased from other stores play on all other MP3 players, but always make sure to check a service's Web site for compatible devices.