Freeplay Music is a user-friendly downloadable music site where music is sorted by genre. There is a search function, but since most of this music is labeled by genre, searching for a specific title is rather pointless. I used this site most when adding music to youtube.
Jamendo is a source of free and legal music downloads. The music on Jamendo comes from the artists who upload it themselves. While not all of the music is licensed for re-use, there is a substantial collection of music labeled with a Creative Commons license.
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8notes.com has sheet music and downloadable drum riffs and mp3's. Not a huge selection (and quite random what you may find here), but you can find some gems here too.
Incompetech is a royalty-free music download site with almost no structure to it. However, you can find some pretty cool music here, if you don't mind scrolling down one huge page. You might be able to find some music by the genre/feel you are looking for using Ctrl + F to open the 'find-on-page window.