While music recognition is now built into Windows Phone 7.5, there is still a place for 3rd party apps who try and do it better.
SoundHound, previously Midomi, has just rocked up in Marketplace, and claims to offer:
The app has the built-in functionality beat by recognizing songs even when hummed, and appears to have a larger database, recognizing even obscure songs.
It features Mango functionality, such as being able to pin the recognition module to your home screen for speedy access, and allows music to be purchased via a Marketplace search.
The app is free and can be found in Marketplace here.
Thanks Haikal and JP for the tip.