I use Gerber's Graduate Puffs... many many flavors to choose from and there's over 400 pieces in a container and they cost between $2-3 at WalMart. My pups were a bit slow to take to them but now they love them. They make flavors like Sweet Potato, Blueberry, Apple-cinnamon, Peach (Sapphire's fav), Banana and others, and mostly all natural.
Plus, if you get hungry, you can eat them too! (also great for enticing the pups to want them!)
Low calorie, no fat, and not enough nutritive value to mess up their regular diet.