I would say the Triathlon Bible by Joe Friel. Good book dude...

Mark, I gotta say man you make some off the wall comments sometimes dude. Do you really beleive that a book won't help and he should only get a swiss ball?

Thanks for the shout out, Tamara. I still do that routine twice a week, and my core is rock-solid.

I was looking for something similar to incorporate into my regular training.

I purchased the Troy Jacobson Strendurance 1.0 - 12 Week Strength Development Program video and have been doing that now for 3 weeks. It's a progressive program, so the initial workouts are 20 minutes and move up to 30 minutes. The number of reps / time / weight increases a time goes on. Easy to follow but that doesn't mean it's an easy workout, the initial 2 week workout was tough.

I also got the Mark Verstegen book called Core Performance Endurance. He does have some go core exercises in the book and some other good useful information. I incorporate some of the exercises from this book in with the video.