I spend a lot of time researching music for videos that I produce, so I thought I'd share my top three websites for very good, license-free, legal and free (or cheap) music. Be sure to check that the songs you're downloading are Creative Commons licensed in a way that matches your needs.
Pond 5 - http://www.pond5.com Price: $2 and up Selection: Excellent Searchability: Very easy Comments: One of the easiest-to-navigate and best music websites out there. Keyword searches are pretty accurate in bringing up songs that match what you want. You can sort through songs by length, sales history, price and several other factors. The music player loads quickly, so you're not waiting forever to listen to a song. You can organize songs into bins that you name (this option requires creating a account). Pond5 is especially good when you need music of a certain length.
Free Music Archive - http://freemusicarchive.org/ Price: Free for non-commercial use Selection: Good Searchability: OK Comments: There are many wonderful gems in the Free Music Archive but it takes patience to find them. I've had the most luck by listening to selections on FMA's music for video blog. I've found that searching by keyword isn't very accurate. When browsing the FMA's whole catalog, I end up using the pre-selected categories like "classical" and "instrumental," and then listening to many, many songs. It's worth it.
Jamendo - http://www.jamendo.com Price: Some songs are free for non-commercial use Selection: Excellent Searchability: OK Comments: A huge selection of songs of all types and quality. Using the "advanced search" option is key so you can weed out songs by keyword, Creative Commons license type, language and artist country. The music player loads much more slowly than on Pond5 and the FMA. I find this site is best when you have a lot of time to research music.