Flaxseed oil is really good for their coat, skin and eyes. (Plus, new research suggest that it is beneficial in preventing certain types of cancer.
)
You also could try glucosamine...either by getting a food that contains it or adding it to their diet as a supplement. It is good for their joints and their coats. Just be careful w/ it as it could trigger an allergic reactions w/ dogs that are sensitive to shellfish.
(Learned that the hard way.
)