For any musician to excel I believe music theory is imperative, not an option. A little tool I think can be helpful to the beginner on up is the website musictheory.net
This site offers Lessons, Exercises and Tools to assist students with their questions during those moments when we may not be available and the online version is FREE. As a bonus there is No ads to disrupt your train of thought.
There is also an iPhone, iPad & iPod version available at a reasonable cost on iTunes.
- Theory Lessons
Is an enhanced version of the lessons. The 39 lessons are presented in their original, animated versions and take full advantage of Apple’s Retina displays.
Is an enhanced version of the exercises and calculators. Each of the fifteen exercises and five calculators uses a friendly touch interface that is fully optimized for all screen sizes across all devices.
Check it out today and let me know what you think.