First...

The rules for being in Brawl are actually:

1. Character must have made at least one appearance on a Nintendo console
2. Character must have originated in a video game (so, no anime/manga/book/etc. characters)

Anyway, the following would be excellent additions

Sonic
Diddy Kong (C'mon, there's absolutely no reason why he shouldn't be in Brawl)
Ridley (See Diddy)
Geno (See Diddy)
Vaati
Tom Nook
Lucario
Deoxys
Starfy
Ike
Sigurd
Lyn
Hector (Who is from Fire Emblem 7, not 8)
Little Mac
Krystal
Wolf O'Donnell
Lucas
Crono
Bomberman
Mega Man
King K. Rool
Isaac
Mike Jones
Sukapon
Balloon Fighter
Poo
Black Shadow
Samurai Goroh