Oatmeal on cold mornings is always nice, you can mix in raisins, bananas, butter, brown sugar, any number of things. Fills them up.
Eggs, scrambled with tomatoes or bacon or even baco bits, quick and good. Hard boiled eggs are good too (just shared some with my daughter (4) and she loved them).
I put sliced banana in her cereal and call it 'banana surprise' to make it interesting for her. She never knows which spoonful will bring up a bit of banana and she is always pleased to announce when she has found the banana surprise.
Beans on toast works too.
Any amount of sliced fruits are good, oranges, apples, whatever else is in season.
Pancakes, which are handy because you can buy them in packs here already cooked, just pop them in the toaster and slab some butter, jam or syrup on them.
For a treat I pick up donuts from the grocery, or we walk to the corner shop and I let her pick out a fresh pastry and one of those Yahoo milkshake things, which I cut with milk when we get home, and sometimes heat up for 'hot chocolate'.
Just some ideas.