I worked through this theory book in college and than went on to study at the school where the book was written. I found this to be very helpful and it includes many exercises you can do to test your skill level. Here is a link below where you can buy the book from amazon.com, as well as seeing reviews.

http://www.amazon.com/Harmony-Theory-Comprehensive-Musicians-Essential/dp/0793579910/ref=sr_1_2?ie=UTF8&s=books&qid=1263175334&sr=1-2