Here are some suggestions my midwife gave me:
Blueberries, fresh or frozen, no more than one cup a day. (I swear by this, as will any other parent of a blueberry eater!)
If you choose to do dried fruit, do stew it first, otherwise it will pull more water from the colon. Raisins, too, require some plumping up first...
Steel cut oats are a great way to plump up those raisin as well as a good source of fiber. You can also add in flax seeds for added fiber.
Also, you can make a smoothie with psyllium seeds in it. Psyllium is a natural laxative; you can buy whole psyllium in bulk or at health food stores.
Foods to avoid: bananas, white rice, pastas, cheeses, white bread, peanut butter-- anything constipating.
And as everyone said, lots and lots of water.