The following characters I see as not only hardcore cool but having great potential for move lists. They also come from games which have few characters already in SSB. Solid list:
Ridley - Metroid villain.
King De De De - Penguin from Kirby.
Meta Knight - Kirby Villain.
Samurai Goroh - Captain Falcons rival from F-Zero series.
Pit - Cupid like hero from Kid Icarus. (classic)
Poo - Kung fu prince from Earthbound.
Jeff - Ballistics expert from Earthbound.
Paula - Psychic powerhouse from Earthbound.
Possible list:
Wario* - Anti-Mario with a very good series of his own.
Waluigi* - Required for balance if Wario is included.
That is my list although I'm sure the game will have many more characters.
* The Wario brothers don't really look right, but I'm sure HAL could evil them up a bit.