Not all dogs need sunscreen, after all that is what their fur is for, but if you have a short haired white dog he or she may be getting burned through the fur. And pink noses and ears are often burned by the sun causing soreness.
This sunscreen is specially formulated for dogs and is the equivalent of a SPF15. It is a spray on formula, easy to apply and, unlike human sunscreen it has no toxic ingredients, so your dog can lick at it with no ill effects. This is quite a small bottle at 4oz, but fairly inexpensive and definitely worth it for keeping soft pink noses safe from the sun.
Costs $7.99 from Amazon.com