I may be a bit partial, but I actually completed this book before I went to MI, as it was used as our curriculum for a Music Theory class at Indiana University-Kokomo where I went to school from 01-05. I feel it does a great job of explaining the concepts as well as providing you with a workbook where you can test your skills. I found this to be very helpful, however; it may not be the best for very, very beginners. Take a look and see what you think.

http://www.amazon.com/Harmony-Theory-Comprehensive-Musicians-Essential/dp/0793579910