Where would be the best/definative place to look up the genre for a particular song or maybe even a whole album?

I'm using cdnow when I can but I notice it's pretty generalized and doesn't always match that of either the mp3's original tag and/or another sites genre listing for the song. Is there one definative site that has the exact genre for just about every song or can this type of thing get too opinionated for there to be a definative answer for some songs?