I guess all dogs are different and you have to find out what each individual likes best. Agree you need to be a little careful with small pups to avoid tummy upsets, and try to avoid the"products" which have too many additives and, guess what, SUGAR!!! for heaven's sake

Suggestions are: liver, chicken, cheese, sausages (cooked cocktail ones); cooked hot dogs, dried tripe and meat (Webbox - try Sainsbury's.)
My dog likes Scmackos (sp?) but they were not enough to motivate in a training class environment, for that she needed cheese etc ;)
Lindsay