Add about a Tbsp of flax seed (ground) to a daily smoothie or anything. It has good, natural fiber that will help keep things moving.
Also, just making sure you have enough fiber daily (from veggies, fruits and whole grains) will keep things clean the natural way.
As for "body cleansers," there are some detox tea that work very gently on the intestines, but also (very importantly) on the liver and internal organs, like "Daily Detox." Just be sure to avoid ingredients like senna (as Laura mentioned), goldenseal (which shouldn't be used internally, according to Andrew Weil, but is great topically for skin problems), or other harsh herbs.