Contains Spoilers!!!
There are 35 characters in the Super Smash Bros Brawl Roster, some with alternate forms (marked with a *). The Characters are the following:
Newcomers
Pit
Wario (Both WarioWare and Wario Land models)
Ike
Pokémon Trainer*
Diddy Kong
Meta Knight
Lucas
King Dedede
Pikmin & Olimar
Veteran Fighters
Mario
Link
Kirby
Pikachu
Fox
Samus*
Zelda/Sheik*
Bowser
Donkey Kong
Ice Climbers
Yoshi
Peach
Secret Characters
Ness
Luigi
Ganondorf
Snake (newcomer)
Sonic (newcomer)
Toon Link (semi-newcomer)
R.O.B. (newcomer)
Falco
Wolf (newcomer)
Captain Falcon
Lucario (newcomer)
Jigglypuff
Marth
Mr. Game & Watch
Transformations
Sheik/Zelda (Zelda/Sheik)
Zero Suit Samus (Samus Aran)
Squirtle/Ivysaur/Charizard (Pokémon Trainer)
Test Characters
Wario Man
Giga Bowser
Red Fighting Alloy
Blue Fighting Alloy
Yellow Fighting Alloy
Green Fighting Alloy
Note: Secret Characters are both new and veterans
Note: Test characters were found when ripped from the game disc. These characters were tested in beta, but remain unusable in the final game. Giga Bowser and Wario Man are transformations via Final Smash, but cannot be chosen at the character select screen, and can only be played as for a limited time. There is no way to unlock these characters, and can only be played with by hacking the game.