Those are pretty funny. I might have to steal a couple.
Edward: Cinnomon Toast Crunch, probably because I am reading the fanfic "Stay" and he likes them, (but they do go along with the whole sparkly sugars).
Jasper: Frosted Flakes. They are classic cereal with a punch (Not really but they are delicious).
Alice: I also agree with the fruit loops.
Emmet: Lucky Charms (I guess that could work for Alice too).
Rosalie: Special K with Strawberries. Those seem to fit her pretty well.
Carlisle: Honey Bunches of Oats. Enough said.
Esme: Cherrios with sugar put on top and maybe fruit in there with it. It's what my mom eats. lol
And even though Bella is technically not a Cullen (though I liked Breaking Dawn, don't kill me, I refuse to count her in the family):
Bella: I totally agree with the boring raisin bran, but I'm not even giving her that. Just plain Bran.