I used to use Shazzam until it started charging. I wasn't going to be able to keep it under 5 songs a month.
I just downloaded "SoundHound" and it is AWESOME.
Not only does it recognize songs (just like Shazzam), but it also recognizes songs when YOU sing them, or even when you hum them!
It's perfect for when you are trying to think of "that one song" and you only know the tune.