Momixa - Pick two songs and get the perfect mix
PlaylistMap - Connect with Spotify playlist curators from around the world
Liveset Database - Database site with tracklists from Dj sets
Lazyset - A Spotify playlist mixing Facebook Messenger bot
FIEND.fm - "Hot or Not" for music discovery: 2 hrs of tracks in 2 mins
Playlist Machinery - Tools that help you create & organize your Spotify playlists