I know a lot of us are learning and using music theory to a certain degree. I also know that there are a lot of sites including this one with lessons and supplemental material. Basically, I am asking that if you know some of these sights, post them here.

Here are a few (other than UG of course that I have found.

This site is a lot like UG, but it has a lot of articles on everything from power chords to advanced theory.

This one is still in the process of construction, but it looks promising and has some great material on modal theory.

This is one of my favorites. It goes from the beginnings of written notation to the most in-depth theory. It also has many useful trainers and utilities such as staff paper generators and chord calculators.

If I were you, I would also invest in some books on music in general. Some high schools like mine offer theory classes as well.
"I worked hard. Anyone who works as hard as I did can achieve the same results.” ~ Johann Sebastian Bach