allmusic.com
This site has endless articles on artists, bands, genres, and even reviews of specific albums. Though listening ability is not guaranteed, this site is a great resource for finding out contemporary, influential, and musically similar artists. Just type in the name of your favorite song or band and start exploring!
Pandora
Pandora is a great tool for finding music because it’s designed to find music similar to music you already like and lets you listen to the whole song. The interface also provides a quick buy link (for iTunes and Amazon) for each song as it plays and a search option (under “About the Music”).
eMusic
Though you must get a monthly membership to download from this site, it has an extensive blues collection, and relatively cheap rates ($.50/song on average).
iTunes Store
Odds are that you’re already familiar with this music purchasing option, but you may not know how to use it most effectively for finding music to download. The drop-down arrow next to the “buy” button provides an option to find other versions of each song, making it easier to find your favorite version of a song. Also, pay attention to the suggestions provided when you buy something.
Amazon
Amazon has an extensive library of mp3 downloads available, and sometimes you can find songs not available on iTunes. Additionally, Amazon gives the option of buying whole CDs for songs you can’t find in digital format, often for very affordable used prices.
Rhapsody
A $10/month Rhapsody subscription includes constant access to a 12 million song library. Because the website is set up well for browsing and allows you to listen to the whole song without buying it (limited number of times if you don’t have a subscription), it works very well for finding new music. However, if you plan on using Rhapsody’s software to DJ songs from their library, bear in mind that you will need a reliable internet connection at the venue (not always guaranteed), and that there are often bugs and glitches that make it a bit frustrating.
CD Baby
If you absolutely cannot find a song anywhere else, chances are you might be able to find it on CD Baby. This website only sells music that musicians send them directly, making it a good source for music that isn’t as well known. Also, they pay musicians directly, so that’s neat.