iTheory is a free ear training tool for your iPod. It took me a couple of tries to get it installed correctly, but it works great. The interface isn’t as clean as I would like. You have to scroll past hundreds of notes before you get to the iTheory main menu. But once I got there, it worked like a charm.
Basically, you just copy the text files to your iPod’s notes folder and copy the MP3s to your music library. Then, in the iPod’s notes menu, you navigate to the main iTheory note and you can test intervals, scales, chords, and absolute pitch.
I think I’m going to hack into mine and personalize it a bit more. It’s really cool how you can reference audio in a note. I wish I knew before that you can do that. My mind is racing with ideas to use this trick.