Spotalike - Spotify playlist with similar songs, according to Last.fm
Bookmark It - Create awesome notes on YouTube videos
MusaicFM - An iTunes like screen saver based on Spotify and Last.fm
Bookmark OS - Bookmark OS is like Mac or Windows optimized for bookmarks.
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...
Siimpl Bookmarking - Start collecting and organizing what interests you