Busy Buddy Bristle Bone
Premier Pet's Busy Buddy Bristle Bone provides a good workout for dogs that like to chew.
The durable rubber bone sandwiches nubby rings, replaceable rawhide treats (or you can be creative and make your own), and bristles that clean your dog's teeth as they chew. Because the treats are wedged in the middle it takes a while to make much progress, providing entertainment and cleaning their teeth at the same time.
The Bristle Bone retails for around $15 (for the medium size) and is available at Amazon and many other online retailers.