We have an Australian Shepherd. Regular teeth cleaning and hard texture treats insure that her breath is pleasant.
The dog mints they sell at the mall and pet stores really help. They come in a little tin and they usually keep them by the check-out registers.
I own a terrier who has had issues with bad breath. I bought a doggie toothbrush and toothpaste at the pet store and it has helped her breath.
I gave my pet Golden Retriever garlic and fenugreek tablets. I bought them at a pet shop and gave my dog one a day and in about a week his breath was back to normal.
also see 4 Ways to Brush Dog Teeth
also see Finding the Right Dog Dental Chew