fiber, lots of water, and of course, coffee!
i've also found that a bit of spirulina can help as well...and for those of us having trouble getting fiber in their diets, they make all that lovely fortified pasta now...i've also found these bars:
High Fiber Bars | 50% of your Daily Value in 1 High Fiber Bar | Gnu Foods
they provide a high amount of fiber, and they actually taste pretty good!