These Musicians or Sound Artists offer their music, often under a Creative Commons License, for your reuse
DanoSongs.com is the website of Dan O'Connor. He posts his original music as free MP3 downloads. If you credit him as described in the License FAQ you may use the music royalty free in a video, game, film, presentation, slideshow or website. If you prefer to not provide credit you can donate at least $10 US per track or buy "the package".
incompetech.com is the website of Kevin MacLeod. He posts his compositions and recordings as free MP3 downloads. If you credit him as described here you may use the music for free. A no attribution form is available for projects where attribution is not wanted or is otherwise impossible is available for a fee. Search options include Genre/Feel, Collections, and Track Name.
PacDV provides a variety of 'free sample' sound clips for you to download and use free of charge in your video, film, audio and multimedia productions, provided that you do not re-sell or re-license the sounds to anyone else, or post them on a web site for download, or link directly to individual sound files. All we ask is that you link back to our site or mention "Music/Sound by www.pacdv.com/sounds/" in your credits. Categories include: Ambiance, Domestic, Interfaces, Machines, Mechanical, Miscellaneous, Music, People, Transportation, and Voices
Partners in Rhyme advertises their services by offering a selection of "free royalty free music" that may be used in Youtube videos and commercial projects completely free of charge and without every having to pay royalties. The music is created and owned by Partners In Rhyme and will not trigger any third party copyright notices. They also have some free sound effects and free video backgrounds.
RoyaltyFreeMusic.com advertises their services by offering 50 "free royalty free music clips" that can be used, without limitation, in Educational, student and personal, not-for-profit projects, free of charge.