If you like circuits, go for Drill Max (my FAVE!), Low Impact Circuit, the Bootcamp/Muscle Endurance DVD and I'm going to throw in the 4 Day Split series as well. It's Cathe's most versatile workout I think. There are dozens of premixes that include some great circuits. But there's also some great, short cardio, some great weight work and awesome ab work.
I used to only do circuits as well (just preffered them and thought they were the most effective for me). I want to let you know, though, that you may be amazed at the results you see from doing Cathe's weight training workouts. Her Gym Styles series is so phenomenal, as is the 4DS weight work, and Pyramid Upper/Lower Body. These were life-changing for me once I gave them a chance. People tried over and over to get me to buy these and I just wasn't interested in weight work--I preferred to stick with circuits. Once I made the decision to give them a try, I was floored with the results I saw and how great I felt.
Just a thought.