Cereal is good in organic low-sugar form. If you're buying major store brands, full of sugar, preservatives and other junk like high-fructose corn syrup, then it's not good for you.
Kashi Golean is not a bad brand, check the ingredients to see if it has any hydrogenated oils or high-fructose corn syrups. If it doesn't you can get started with it. Ideally, you want a high-fiber low sugar cereal.
I read somewhere that you want a cereal (like Mr. X noted) without any high fructose corn syrup, and overall a sugar content of less then 5 mg.
I've found that Cheerios & Rice Chex have minimal sugar (I think 2-3mg), no high fructose corn syrup, no fat, carbs around 26-30g and 1-2g fiber. Good stuff with some splenda and skim milk.