A beignet is a New Orleans treat--puffy squares of fried dough (kinda like a donught or funnel cake) usually topped with powdered sugar.
My favorites:
MK: Dole Whip and giant chocolate chip cookie ice cream sandwich. I ate the later for dinner and still shared part of it with my Pop. Seriously huge and a snack credit!!
EPCOT: There are lots of awesome options--not sure I have a favorite.
DHS: Starring Rolls cupcakes--chocolate filled with peanut butter
AK: I am usually saving myself for dinner at Boma, but I do love the frozen lemonade here as in all of the parks and the frozen chai is good.
And I agree with the PP about the chocolate cake at many CS locations. It is always moist and very chocolatey.
My favorite dessert is the butterfinger cheesecake from Sunshine Seasons in Epcot. Not sure if you can us at snack credit for it, but honestly I can't see why you couldn't (but I don't know for sure!)