I visited the last.fm/audioscrobbler folks today, to catch up with them (it's been a year since I last went over there). They've added several more people, and I was happy to hear that they've got several revenue sources (ads, premium services, research data) so they're staying afloat (growing, in fact) without taking in evil investor types.
I had asked them last year if they could give me "people who like (name of magnatune artist) also like (names of major bands)" so that I could input this data into a soon-to-be-released search engine on Magnatune.
Well, they've done that, and a lot more, with a beautiful implementation of a web-services API, all based on REST. I had argued strongly a year back to avoid doing complicated SOAP services, as these are a pain for the client side, instead allowing simple parameters-in-the-url and returning simply formatted XML docs. That's exactly what they have, and it's gorgeous.
For an example, visit this URL which returns XML sounds alike for Magnatune artist Brad Sucks.