I learned so much from the following book;

Harmony and Theory Workbook: MI Press

I actually did most of the book before I attended Musicians Institute in 2005. I found this extremely helpful, and it moved at a good pace for me as at the time I had an OK grip on theory but needed a workbook to actually apply it. I can't say enough great things about that book and how it helped me. It has also helped thousands of others around the world.

- Douglas