Apple Jacks: "It doesn't taste like apples, we eat what we like." That doesn't even make sense, but obviously the marketing worked.
Captain Crunch: You'd think he's be promoted to Admiral Crunch by now...he's been captain of a cereal for the past twenty years. And his eyebrows are on his hat.
Cheerios: If you've ever seen Superman (the movie), you'd notice the box of Cheerios strategically positioned in front of the camera in the scene before he leaves home. It's probably one of the first and most effective examples of cinematic product placement (aside from Coca-Cola, of course).