In my mind has always been Michael, what about you?
EDIT: Let's now say this also goes for E Honda and T Hawk. I'm thinking Edward and Tim.

Mighty

Masturbator

Magic

It's mike.

It is Mike because of the whole lawsuit from Mike Tyson thing, but Michael does actually have a nicer ring to an evil dictator. 
 
Personally I'm glad it's Bison over here. Vega always sounded like a pansy name.

Mike Bison. It's meant to be reminicent of Mike Tyson. The famous boxer.

Mison Bison.

Molly Bison.

Mister.

Ol Matty Bison.

Michael. Because its fucking hilarious.

VEGA!!!! HIS NAME IS VEGA!!!

Milton. Stapler.

Mandy Bison.

This thread is awesome.

Miss Bison... 
 
 
 
From what I know, originally it was supposed to be Mike Bison for the boxer in the Japan release of Street Fighter II.  Then the boxer became Balrog and the dictator got the M.Bison name for Major Bison.  Something like that.

Marvin.

Miranda Bison.
 
Y'know the 80's shoulder-pads were kinda a hint.

Minty

Mandy

Morton

Mother-effing Bison. Nah, I would say Mike Bison.

Melvin

Marilyn

Marsha

Manfred Bison and Tony Hawk

Martin Bison, Lil Timmy Hawk and Egbert Honda.

Since M.Bison is the Boxer in the original version, it's Mike Bison.
 
The dictator we know is actually Vega.

MMMMM Bison

Mylanta Bison

Epic Honda, Theodore Hawk, Magnetic Bison or Magistrate Bison.

Anytime someone's first initial is M, their name is Magic. It works no matter what.

Mison Bison duh 
 
Edit: damn it someone beat me to that :P

" Morton "

" I believe E.Honda's first name is Edmond. I think I remember seeing that in the instructional manual of the Street Fighter II World Warrior for Super Nintendo. "

 The T in T. Hawk stands for thunder. Not joking. 

They parodied Mike Tyson, so obviously M. Bison the M stands for Mike. E. Honda is Edmund, and T. Hawk is Thunder.