Commercial music

The majority of music released under a CC license uses one of the licenses that prohbit commercial use (for purposes of verbatim distribution this includes all of the "sampling" licenses, even ones that allow commercial derivative use). There is as yet no web-scale audio-specific CC search, so here are some pointers to finding music that allows commercial use at some of the CC content curators.

ccMixter

http://ccmixter.org/media/tags/attribution -- all tracks under a plain BY license. Add genre and other filters to the list by clicking '+' next to the desired filter on the right.

Jamendo

http://www.jamendo.com/us/?p=music&tag=&l=all&o=rating_desc&cani=c&aclass=2+3 -- Jamendo-specific search that only displays albums permitting commercial use. Fine tune search by adding keywords or changing the sort order in the form on the right.

Others

Many other sites host music permitting commercial use, http://archive.org in particular. Add instructions here for finding only commerce-allowed music at these sites.