Fruit is a good idea if your dog isn't sugar-sensitive. Apple chunks, banana slices (fresh or dehydrated), mandarin orange slices, blueberries, and melons are all good choices.
If you want something store-bought, I've never met a dog that didn't go bonkers for dried fish skins. They're crunchy, low-cal, and you can break them up into whatever size treat you need. I've no idea why they're so pricey on Amazon; I get this exact brand at my local doggy bakery for $8 per container.