I agree--my routine is very similar to Debbie's meaning I do many of the same exercises, & also that I don't really have a set routine. While most of my weight training is set in stone, my core training is different every week.
That said, I ALWAYS have at least one weighted routine a week. Usually it's at the gym, & Core Max sec. 3 plus one of the other sections. I try to fit in a 3rd pilates workout at some point, or Ab Ripper X which is great when you're short on time but looking for something intense.
I also agree that kickboxing is a great cardio workout that incorporates the core. In fact it's the staple of my cardio.
However, the one thing you don't want to do (I think) is overtrain your abs. The days of 300 crunches 6 days a week are over. Of course this depends on the look you want--if it's a flat, lean stomach then overtraining isn't necessarily a bad thing. But if you want a defined, "six-pack" type look, working with weights is essential, and keep your ab workouts down to 2-3 times a week.
And diet, diet, diet.