Whether for humor or not. A few I thought of:
Jame Earl Jones: Who could argue with that bad-ass?
Harvey Keitel: I’d like to see his press release about being caught with an intern. 
Gene Wilder: He was just so cool as Willy Wonka! Plus, he seems like a truly nice and caring guy.
Courtney Love: See James Earl Jones.
Who would you like to see?
Clint Eastwood.
“So, punk, did I fire five nukes or six? Were you counting? Do you feel lucky, punk, do ya?”
Charlton Heston - who’d screw with Moses for goodness sake - a president with smite power.
I’d like to nominate Robert De Niro:
“Hey, Slobodan, you talkin’ to ME? Are you talkin’ to ME?!?!”
Foreign powers would tremble before the might of Jake La Motta 
As long he’s a citizen - the Taco Bell dog
Pee Wee Herman - whenever anyone criticizes the USA, he would come back with “I know you are, but what am I? HA-HA! ARRRR!”
Silent Bob.
Whaddya mean he’s not a real person?
Damn! Friedo took my answer!
Clint Eastwood would be too cool in office, I also liked the idea of Charlton Heston.
As long as we’re listing bad-asses, how about Samuel L Jackson? This guy was Shaft and Jules in Pulp Fiction, there’s a pair of characters you don’t wanna piss off.
Do they have to be alive?
I would really, really like Jerry Garcia to be President of the United States.
Actually, I would like Jerry to be King of the World.
Emilio Estevez He’s a great director, plus a warm guy.
My choices are not so much who i would like to say, but more of what I believe are strong possibilities.
Tim Robbins
Clint Eastwood
Robert Redford
Robin Williams
Tom Hanks
Harrison Ford, no doubt.
Emilio Estevez
Alec Baldwin
Sam Neill
-SSB
Harrison Ford. He is a real grounded, caring individual. He’s also pretty intelligent.
Tommy Lee Jones, I think he would kick ass as Prez.
Alec Baldwin??
Alec Baldwin ???
***Alec Baldwin??? ***
He, of the “go and stone Henry Hyde and his family” fame???
Tell me you’re kidding, please…
Zev Steinhardt
Henry Rollins, no question about it.
Gallagher
And possibly Sheryl Crow
Richard Petty (The King of Stock Car Racing) – so we’d have a king. also he doesn’t take shnit and he has this kind of down-home country boy logic to him.
B.B. King – see the first part of Richard Petty
The guys from Ben & Jerry, one as Prez and one as Veep
Not to mention a Jedi Master.
Dennis Miller. I mean, come on! He’d just confuse anyone who pissed him off with obscure references.
Alan Alda.
He is so caring and sensitive and understanding. We could open our arms to all the nations of the world and have a planet-wide hug.