I don't know if I should post this here, but I use this
to figure out the key signature of a song.
It's a mp3 to midi converter, but the conversion is horrible, so it's useless for picking up notes. However, it does tell you what key signature it's in (I don't know how accurate it is, considering I don't have perfect pitch.)
Oh, and the free trial only lasts 30 days, but it still has enough features after the free trial to be able to use it for key signatures.