Kashi has a lot of good cereals that are actually really damn good for you too. Their non-frosted 'mini wheats' (the name escapes me) has two really good flavors at least and you can get some pretty substantial protein out of their soy cereals. Beware of gas though.
Man as a kid I could eat Waffle Crisp until I exploded though. I also really liked Golden Crisp, but I haven't seen that in ages. Corn Pops could be really good but they're so unsatisfying because they're like 75% air.
Oh and Quaker Oatmeal Squares are pretty awesome.