Gracenote "touches hundreds of millions of music fans and TV viewers everyday. The Gracenote database is the largest source of music and video metadata on the planet, featuring descriptions of more than 130 million tracks and TV listings for 28 countries." Recently, Gracenote launched a developer program that opened its Gracenote API to the developer community. The API delivers Gracenote's rich music metadata to any connected app.
Peachnote is quite an innovative approach to music analysis. Developed by Vladimir Viro, a renaissance man who bridges the worlds of classical music and advanced mathematics, the Peachnote API provides the ability to search a large collection of public compositions by melody or sequence of chords.