I was never a fan of Boo Berry, but for a while there I ate a lot of Count Chocula and Franken Berry. The Monsters Cereal blog has everything you need to know about those guys. I too wonder why we don't see ads for these guys anymore (though I haven't watched Saturday morning cartoons in ages so who knows.)
Wait…there was a cereal called Yummy Mummy? That's hysterical.