My girls have weetabix, porridge oats, shreddies or crunchy bran. We do have Special K as a snack but they only have that as a treat occasionally (it's sweeter than the other cereals we have).
If we are in a hotel (like once every 6 months!) they might have rice crispies or cornflakes but they're not really that fussed.
I lived in the states for a while and adored Cap'n Crunch! Dread to think how much sugar is in that.