Epcot - Fish Shop at UK, bakery in France (there are meal items here as well as bakery), Sunshine Seasons in The Land.
MK - Columbia Harbor House and various other carts stationed around. We couldn't find the sugared almond carts or the egg roll wagon on this last trip but those were delicious snacks!
MGM - eh, tough to find stuff here but they have a hot dog stand that's ok.
AK - Flame Tree BBQ is a WONDERFUL counter service place. There's also a great little fruit/vegie cart over in Harambe just outside the entrance to the Safari.
Those are just a few off the top of my head.