Becky,
I find that increasing fiber and water (within reason) helps a lot. My IBS has me swinging between extremes, so I REALLY try to be consistent with my fiber and water. So far, I like Kashi Go Lean as my main source. I aim for 30 grams of fiber a day, but don't always make it.
Another thing that may help is ground flax seed or flax seed oil. I take one tablespoon of flax oil a day, and I think it makes a real difference. It also seems to help my dry skin issues if that's any incentive.
Obviously, exercise can help, too, but if you're posting here you've probably got that angle covered!
Good luck -- this is a real bother! :-(