I'd recommend a raw bone as well. Marrow bones are good (and you can easily scoop the marrow out if you think it might be too rich for your dog), shank bones are good, knuckle bones, etc. You just have to watch weight bearing bones as if your dog is an aggressive chewer (ie: chews very hard) they might chip or fracture a tooth. Though that can happen with any bone really. Dance (my toller) fractured a tooth on a nylabone of all things. Rib bones are good as well, but are different as they do actually eat the bone, whereas they can't get through/eat the weight bearing bones. You can get most of these at a grocery store, a butcher, and many pet stores that carry raw dog food.

If you're looking for something more as a treat type thing that he can actually eat that is not a bone, Bully Sticks are a great option. My dogs love them and while they don't last overly long (45mins at most for my guys), they do keep them occupied for a little while and tire them out a bit.