One (for me) really cool feature in other music players is integrated support for finding similar artists to what I'm listening to. I can sit down with Spotify and browse around and find a lot of new favourites. Obviously there's a difference that Spotify can play all these immediately. But still, finding new favourites is something I enjoy a lot. So obviously I love the AMG, Wikipedia, Last.FM and Amazon buttons in MC
Here's another "find-similar" provider:
http://music.biograph.be/