If you fancy cooking muffins are great for breakfast, or pancakes or scones, you can make them with fruit in if you want, banana scones are lovely. Do all have a bit of sugar in though.
You could do a home made muesli with loads of different types of fruit and little / no sugar?
My DS loves a big plate with a mound of natural yogurt in the middle, surrounded by circles of grapes and slices of apple or pear and drizzled over with honey or maple syrup.
My DD likes beans on toast or cheese on toast for breakfast (& lunch and dinner if she can wheedle it).
A breakfast omelette or scrambled eggs are healthy and tasty too. On Sundays I sometimes do a mock Spanish omelette with potato and onion in - I make sure I have a few ready boiled potatoes in the fridge by cooking too many on Saturday.
Cereal wise we stick to Weetabix, corn flakes, rice crispies and raisin wheats. Plus porridge, DS likes it with stewed apple or other stewed fruits on top, also you make it with part fruit juice and part milk - apple juice gives it a lovely flavour.
And mine like popcorn and fruit salad!
By the way, DS (8 yrs old) recently discovered that 4 weetabix a day has a bad effect on the digestion. More white bread recommended as a cure...