senna leaf tea - you can buy it from Traditional Medicinals it's called "Smooth Move" tea - very effective for occasional use After that modify your diet to include plenty of fiber rich foods and drink plenty of water as that will keep you going naturally.
Any food item, which has good amount of fiber. Papaya fruit is quite beneficial to regulate the bowel. Husk of whole wheat, Sat-Isabgol, a natural vegetable product, derived from seeds of Ispagul( Plantago Ovata), is commonly used in India as a natural laxative. It is purified by milling process and packaged. It helps if you have a systematic and regular life, timely meals, healthy diet and exercise. Avoid greasy and junk food.