to me, do-wop is a great great forum for getting a handle on music theory. I used to sit in church and writer the chord progressions in the hymnals. Anywhere you can get a medium to explore music in its interrelationship is a good one. I think the simplist one is standard blues.

I learned to ad-lib on a trumpet playing in a bar while I was in the eighth grade. Had it been more complex music ie jazz, I wouldn't have been able to walk before I ran. Having said this, I still am more in to playing the music rather than analysing it.

The reason I have taken a technical bent in this thread is that it is what the original question was about. I still defer to guys like Jerry who forgets every day more than I will ever know about music!