RFI: Cross streaming service search function

I subscribe to Spotify, am trying the free trial of Google Music and have Amazon Prime. Occasionally I'm looking for something that is on one service and not the other, or maybe it's on a service I don't use. Has anyone come up with a website or app that searches across all streaming services?

Closest I've seen to that is the Sonos app, which searches across all streaming services that you have an account with -- but obviously you need a Sonos speaker, and it won't show what's on a service you don't have an account with.