Another animal that would be cool would be cows. With cows you could actually get real milk instead of butterfly milk. Also you could get cow meat from them and make new foods like hamburgers or tacos. What do you think?
I second the animal that gives you honey. Buying it all the time is a little annoying. Though considering glitch, bees would be too obvious. Ants maybe?
+1 for chocolate giving cow-creatures of some sort (as long as Kukubee can draw an appropriately glitchy cow!) - this is one of my all-time favorite suggestions: