I've always enjoyed music discovery services. When a new service is launched, I've been known to spend hours playing around seeing what new music the service can find for me. So I figured it would be fun to build my own music / artist discovery service (using Google App Engine). I call it Markov Music.
When you type something into the search bar, the app tries to match this search term to a known person. Using the Freebase database, the app then look for other artists that influenced and were influenced by the artist you entered. After showing you a YouTube video of this artist, another artist is randomly selected from the list of influenced and influenced by. And so forth and so on. Hence the name Markov Music - the artist selection technique forms a Markov Chain.