so you're getting good fight endurance just from practice.
to supplement that, I suggest that you immediately buy Ross Enamait's Infinite Intensity or Never Gymless. Do a search on here for reviews of them as they come HIGHLY touted from everybody on this board who's come in contact with Ross or his publications. Vids and sample workouts are on the website.
http://www.rosstraining.com
For some good circuit ideas, you can check out my log, as well as finnegan and Bubble Boy for some ideas for circuits.