Updated: More alternative costumes revealed
A bunch of people on the Shoryuken.com message boards pointed out a handful of videos showing the new costumes. Also AdverseSolutions translated the latest SF Dev blog entry that explains what some of the new costumes are.
Ryu: Worn-out sleeveless gi, exposed at the top.
Chun: Erotic dress.
Blanka: Explorer style.
M. Bison (Dictator): Normal clothes are worn-out, with no hat.
Honda: Decorative loincloth.
Fuerte: Cook.
Rufus: Coat instead of the suit which shows his bellybutton.
Guile: Charlie's clothing.
Viper: Leather outfit.
Zangief: Mike Haggar's outfit.