Music theory was tough for me. I was always a very visual learner so hearing chord progressions and analyzing them were difficult to grasp. A new site I just discovered might have changed all that for me by tying auditory research together with visual representations of that research. Dave Carlton has analyzed the chord progressions of over 1300 popular songs and laid them out in a way that is a great resource not only for music students but also for songwriters as well.
The more I look at this the more I think it would have been WONDERFUL to have had access to something like this in college when I was struggling with these concepts in class. They have a great page dedicated to the basics of music theory in song writing to help you understand chords and progressions even better. For visual learners this is a great music theory resource that you definitely need to take a look at.