Owl Music Search is a cool tool that was spotlighted at a Creative Commons Salon last night. The potentially endangered Pandora and Last.fm recommend which music you'll like by matching text descriptions of albums, artists and songs. But Owl analyzes the actual waveforms of music files and matches them to similar tunes, many of which have Creative Commons licenses.
When I uploaded Leonard Cohen's "Hallelujah," Owl dug up 44 tracks by Loretta Lynn, Outkast, the Rolling Stones, Marilyn Manson and others, highlighting snippets of their songs that resembled parts of "Hallelujah." Owl has the capability to let you select segments of a song and search for that clip elsewhere. In theory, this would let you find, say, which rappers have sampled "Chocolate City" among a gajillion other Parliament jams.
Owl looks promising but is still hatching from its version .3 shell. Its tagline "finding music through music" describes the novelty but also the limitation to its random search feature. While Owl let me narrow down music by year and genre, I found no text search field on its site. Instead, you can search words and phrases within Owl either via Creative Commons or a Firefox plugin. Mac users can also install a plugin to scour Owl via iTunes.