One bowl of a WHOLE GRAIN cereal (bran flakes, total, most of the Kashi's, shredded wheat) either as breakfast or as your before bed snack.
Lot's of water will help as well, actual water, not tea, coffee, milk, soda, juice etc (those do give you some liquid but they also have things in them that can negate the benefit of the water they hold).
Excercise will actually help as well. If we're not moving neither are our insides.
Flax seed will also help.
Those probiotic yogurts will do the trick but they do contain a lot of sugar.
Stool Softners can help, the easier it is to 'go' the more likely you will.
Laxitives are really a slippery slope (so to speak) I would never use them repeatedly unless you are under a doctors care.