There are many all you can eat buffets - most of the character meals, plus some others.
1900 Park Fare @ GF
Boma @ AKL
Hollywood & Vine at DHS
Crystal Palace at MK
Akershaus - part served to you, part buffet
Biergarten
Chef Mickey's
Cape May Buffet at Beach Club
Whispering Canyon at WL has an all you can eat skillet dinner, but not a traditional buffet
I might have even missed some. You can probably search by buffet on the Disney dining site, but I'm not sure of that.