This post was previously on the Pathfinder Software site. Pathfinder Software changed its name to Orthogonal in 2016. Read more.

Music and the web have a long history, from Napster through the iTunes Store to the MP3 blogs of today. For Web 2.0 hackers, however, the availability of public APIs proves pretty hit or miss. Cool mash-ups do exist – for instance, TuneGlue MusicMap, which provides nice visualization to data from and Amazon. But lots of the big music databases don’t offer public web services. Indie download site eMusic used to, but stopped, while big commercial entities such as Muze and the All Music Guide keep their data stores proprietary and pricey. (Full disclosure: I frequently write freelance music reviews for AMG’s sister site, the All Movie Guide.)

If you do a little hunting, however, you’ll discover lots of web services that deliver powerful music content. Licensing terms vary, but the following 15 links should provide enough content to power tons of cross-pollination:

Speaking of RSS feeds, lots of social music sites offer this quick-and-dirty alternative to a real API. Still, others offer tantalizing hints of their future API offerings:

Finally, it’s too early to tell how the APIs coming at us from one social network after another will affect our ability to access music data. Still, between MySpace, Facebook and Google’s Open Social, something interesting is bound to evolve. Perhaps Open Social will allow social music networks such as imeem, Mog, iLike and QLoud to grow past the also-ran stage. And let’s not forget Songbird, the open-source media player, whose own APIs allow all sorts of interesting interactions between services.