I dont think anyone has mentioned the Biergarten in Germany.
We aren't huge buffet fans (we currently travel with small children - I think this will change when we travel with teenagers), but we've eaten at:
Ohana's breakfast at the Poly- all you can eat, but "family style" - no buffet. Decent - if someone mass produced scrambled eggs, bacon, sausage and french toast sticks. Oh and good biscuits and great pineapple coffee cake.
Whispering Canyon at the WL - we didn't get the all you can eat here, the food isn't fantastic, but decent and plentiful - especially if you are big red meat and potatoes people - also served family style.
Boma for dinner at the AKL - an unusual buffet. I wouldn't rave about it as so many people here do, but there is plenty on the buffet - you WILL be able to find something to eat - and something to challenge you. African themed - so lots of grains, beans, salads. But they haven't skipped the red meat and fish. And people say they have one of the best buffet dessert selections going.
Biergarten in Germany at Epcot - German food. Very good spetzle (I'm misspelling that badly). Wonderful cheesecake on the dessert buffet. Hearty food.