We like friendly's for breakfast - I reommend the stack of pancakes topped with cherry or apple and squirty cream, with a side order of bacon (sounds gross, tastes yummy). They do great omelettes, egg dishes as well.
One we go to is on International Drive, near the Mercado area. There used to be one on the 192 near Osceola Mall, but not sure if it closed when the mall closed.
I don't like eating a heavy breakfast and I also strive to be at the parks for opening so we sometimes do this. We always have a drink before leaving the hotel and maybe a cereal bar. It works really well because it also means we don't have to queue as we go for lunch early.
Other times we pick up a light breakfast/snack in the parks.
MK - bakery on Main Street.
MGM - ABC Commisary
AK- Tusker House
Epcot - Bakery in FW.
Dennys, IHOP, Cracker Barrel, Shoneys - we tried all of these this year and they were all fine. Or, as another poster has suggested, get to the parks and have an early lunch. We did that some days too.