I have been using this service since Microsoft picked up on it years ago:
Its called SHAZAM
It works better if you register your mobile number first, as then you can log onto the website and actually see what remix they are playing, if there is one.
If you dont want to register you just play loud music and dial 2580 on your phone and stick it near the speaker. It has never failed on a song yet, just told me the music wasn't loud enough.
NOTE: I am talking from the UK this service