Raw knuckle bones and beef feet. I tried brushing for a while with CET enzymatic toothpaste but it didn't do a **** thing. My dog came to me with plaque build-up that the vet said would have to be removed through a cleaning, but she is working away at it on her own through chewing on bones. Her teeth look great and the last time we took her in they said a cleaning would be a waste of time.
Just beware of tooth fractures with hard bones like knuckle bones and antlers. There are softer bones like feet and necks that you can give, but it is always best to supervise until you know your dog can handle them. My dog is a champ with knuckle bones but she will get rawhide chips stuck in her mouth at weird angles and panic.