Spotify Plus
The developer community is building around Spotify's platform - as noted by their recent community awards. Playlistify was the overall winner, allowing you to convert an iTunes playlist into a Spotify one. Minus the songs they don't have - which is still proving to be their weak link.
You can see a Spotify clickable export of the Chimpomatic master library here. Although it's a couple of months out of date. Will send word down to the tech basement requesting an update.
13th Apr 2010 - Tumblr