The most extreme example I'm aware of is the size of dogs:
a chihuahua is about 4.3 times smaller than a gray wolf in terms of shoulder height, 4 stds of the wolf height. Increasing size seems much more difficult than decreasing it, as the tallest dogs, great danes, are in the same range of wolves.
Some breeds of dogs are shorter and more massive than wolves, but not by much.

Other domesticated species, AFAIK, show much less variance.