Slashdot linked up news of mice that can regenerate just about any damaged tissue:

"We have experimented with amputating or damaging several different organs, such as the heart, toes, tail and ears, and just watched them regrow," [research leader, Ellen Heber-Katz, professor of immunology at the Wistar Institute] said.

"It is quite remarkable. The only organ that did not grow back was the brain. "

Sucks to be that mouse, but remarkable for just about everyone else. The gene combinations that create this effect are "almost certain" to exist in humans. Of course, finding them and then activating them without creating horror-movie side effects are different things. But you have to start somewhere.