Three Dog Bakery's "Itty Bitty Bones" or "Jump-n-Sit" bits are a hit at our house. The bones are about 2/3 the size of a small Milk Bone and the bits are just a little bigger than kibble.
Check out their site and see if there is a store near you.
www.threedog.com
Ozzie likes both the Peanut Butter and the Apple Oatmeal, the latter being low-fat or fat-free (can't remember which).
Oz has a sensitive gut but their all-natural goodies don't usually give him any trouble.