For some strange reason I have always liked this panel from the Masters of the Universe minicomic "The Stench of Evil!" Even though the art is nothing special, something about the structure of the panel showing Prince Adam transform into He-Man with a simple KABOOM! down the middle works really well! I also like the fact that the power changes from orange to a dark red, creating a link to both images within the single panel.
(click on the image to see it at full-size)