Program: Open Pandora
License: GPL
Description: "OpenPandora is a windows desktop application that exposes Pandora music discovery service. OpenPandora fully integrates with the desktop environment and adds additional features to enrich the music listening experience."
Website: http://openpandora.googlepages.com/
Other: It leaves a folder, ApplicationHistory, in the User Profile Directory. I haven't found anything other than that. The registry looks clean, but somebody should double check that.
Edit: Looking at it more it looks like it requires .Net. That's too bad, does anybody know of anything else which could possibly be made portible?