I do a variety of core exercises. There are some tri sites that have a whole bunch of them that I found helpful. Here's one site I use:

http://www.beginnertriathlete.com/cm...?articleid=486

I also do "good mornings" for my lower back and also twists and side bends with weights for my core.

I do these about 3 times a week when I do my overall upper body weights workout.

I have my full body covered when it comes to exercise. I'm not a couch potato who just gets on a bike once in a while. This is my fourth season riding and I've been active my whole life, including weights and strengthening exercises for several years.