My brothers and I are huge huge huge fans of the cinnamon buns at Main Street Bakery, and those are so huge that they could be split between two people. Their muffins are also very yummy!
Cheshire Cafe in Fantasyland has assorted cereals, muffins and fruit, and Sleepy Hollow has both the breakfast waffle and a waffle with fresh fruit and Nutella (not everyone's definition of breakfast, but hey, it's vacation lol).