As a regular part of my daily whistle practice, I pick a tune at random (one I can hum) and try to play it. This is a method of practicing ear learning. Last night I tried The Pogues's Lullaby of London, a song I sometimes sing to my daughter at bedtime.
Wow, that sounds really nice on the whistle! It was very easy to learn, too. Thus far I'm just following the vocal melody, but I'm going to keep fiddling with it.
This is fun, because it's taken a fair amount of work to pick up the other tunes I have memorized now, since I didn't know the tunes well at the outset. But since I've had this song memorized for years and it's fairly slow, I was able to pick it up in about ten minutes. This is a dramatic demonstration of the often-repeated point that the best that the best method of memorizing ITM is to put a CD on auto-repeat for a few days and not even bother with a score.