Mine was Frosted Flakes. Tony the Tiger's "They're Gr-r-reat!!!"
I just loved adding a crapton more sugar to my Frosted Flakes because I was a sugar-soda-high caffeine addicted kid.
I also loved Cap'n Crunch, Honey Nut Cheerios, Rice Krispies, Frosted Mini-Wheats, and Lucky Charms.
What was your favorite Kid Cereal?
EDIT: I forgot about the toys! The toys they put in the cereal box. Just getting the cereal just for the toy inside! That was probably the best part about cereal!