Mostly Aldi or Sam's Club... I buy Life Cereal at Sam's.
Sometimes, I'll pick up something on major sale at Kroger.
We go through a ton of cereal here. I usually buy it at the local grocery store since they have really good sales (5/$10) and I can use coupons that double. Most boxes end up less than $1.50. Of course this is the small boxes but the big ones go to waste because they get tired of it halfway through. I am really really low right now. I have 4 open and 6 unopened. I usually have 20-35 boxes at a time.