[jahern]

I purchased a chromatic tuner (about $20) to see what any note I hear is. For instance, if I see that a high note that Paul McCartney sings is a B flat, I know that I will have to change the song down at least 3 half-steps. (McCartney is a tenor and I am a baritone you see)

This way I know, even if it's early in the morning or I have a cold, if a song is in my normal range.

Using this tuner, if you are capable of figuring out the key note and whether it's major or minor (all you need to do is hum the note into the tuner and it tells you what it is)

Other than that I believe their is Midi software that will transcribe a piece played on a special instrument, change keys etc.