Some things my dog goes nuts for: steamed green beans, pumpkin puree (not pie filling - its spices are bad for dogs), cottage cheese, watermelon, canteloupe, peanut butter.
Someone sent me a doggie cake recipe for my dog's recent birthday. It's a peanut butter and carrot cake with banana frosting - sounds like something my girl will love. I can't post the link (newbie alert, lol) but if you search for "My Dog's Peanut Butter, Banana, Carrot Birthday Cake" you should be able to find it easily.
Have fun with the birthday!