G.I. Joe (Orca and Wolf Transformations)

This is a famous transformation, but I think Daymon is right to recommend posting it anyway.
It's from the season 2, episode 15 of the original G.I. Joe cartoon, titled "Iceberg Goes South."
Cobra ("a ruthless terrorist organization determined to rule the world!") is creating beast-men in the arctic, and Iceberg, one of the Joes, gets captured and transformed into a killer whale. I'm old enough to remember watching this episode when it first aired; this was one of the first transformation scenes to make a big impression on me as a child. 

EDIT: the original links are dead, but all the videos can be seen at Shadowlord Inc. 

Here's the whale TF, followed by the reversion scene. 

And here's one of Cobra's human-animal hybrid soldiers reverting from wolfman to plain man.