Howard Dean
You know why the scream was so funny? Because it was unique enough on its own that it could never be made to sound more outrageous than it was. It's so funny on its own.
Dana Carvey made a living exaggerating Bush 41's over-enunciation and "1000 points of light." If you actually hear Bush speak though, there is a major difference between the way he talked and the way Carvey sounds.
In Dean's case however, any impersonation would run the risk of underplaying the ridiculousness of the soundbite.
But remember, it wasn't the scream that doomed Howard Dean. America could forgive something like that if he seemed like the right candidate.
Howard Dean wasn't.
Still, it doesn't bother me that Dean will only be remembered as the guy who burned out on a cold night in January. If he hadn't done that, he wouldn't be remembered, period.