Epcot has in "the Land" a quick service breakfast. Mostly breads, cereals and pasties. We usually eat breakfast there while we wait for our Soarin fast pace.
MK has the Main Street Bakery! Great food items. My favorite is the Kripy Kream Doughnuts. 2 for $1.99 so it is easy to share. They also have breakfast sanwiches, and yougert.
AK has Tusker House for breakfast.
MGM I think ABC Commissary serves breakfast also.