I wish I could hide the below info so that people who choose not to see can skip it, but I can't. Through Japanese leaks comes the following info:

New Playable Characters confirmed:
Luigi
Captain Falcon
Marth
Ness
Wind Waker Link (Toon Link)
Falco
Lucario
Ganondorf
R.O.B.
Mr. Game and Watch
Jigglypuff
Wolf

It appears that characters will be unlocked by playing and successfully completing said characters storyline in the Subspace Emissary (Adventure Mode).

New Characters confirmed (bosses, assist trophies, etc.)
King K. Rool
Wind Waker Ganondorf / Beast Ganon
Subspace Robots

New Stages confirmed:
Wind Waker Ship
Green Hill Zone
F-Zero GX Aero Drive
Classic Mario Bros (History of Nintendo stage)
Final Destination
Luigi's Mansion

Videos
http://uk.youtube.com/watch?v=bGEXUEdQvKg
http://www.youtube.com/watch?v=58oLpa496aI
http://www.youtube.com/watch?v=pZdr5rHLUl4
http://www.youtube.com/watch?v=1N1yV71AWuc
http://www.stage6.com/user/advent2/video/2149621/Super-Smash-Bros--Brawl-intro
http://ca.youtube.com/profile_videos?user=fairuzons

Super Smash Bros. Brawl ‘final smash montage’ *new
Super Smash Bros. Brawl ‘Snake Vs. Pit’ *new
Super Smash Bros. Brawl ’spoiler’ *new
Super Smash Bros. Brawl ‘challenger approaching pt 3′ *new
Super Smash Bros. Brawl spoiler *new
Super Smash Bros. Brawl *new

Screenshots
http://s259.photobucket.com/albums/hh286/KazeSSBB/
http://gonintendo.com/?p=34396#more-34396

Misc. Info
http://www.neogaf.com/forum/showpost.php?p=9519133&postcount=785

MORE UPDATES WILL BE ADDED AS THEY BECOME AVAILABLE!