The Florida Sun-Sentinel has a truly awe-inspiring series of retro cereal box photos posted on their website. Sure, there's Quisp and and Mr. T cereal, but there are also many I've never heard of. Cap'n Crunch's Punch Crunch. Grins & Smiles & Giggles & Laughs. And, perhaps my very favorite, Crunchy Loggs.
Makes me want to go out and buy whatever movie tie-in cereal is currently available. Maybe Indy's Crunchy Skulls, or Get Smart Shoe Puffs, or Love Guru Fruity Genitalia. Mmm, artificially-flavored corn-puff penises.
If that's not enough, here's another good resource for retro cereal packaging, and another, and this one that's a tad too high concept to be useful, but interesting nonetheless.