My research has led me to a somewhat exotic area: 3-D product shape trademarks. These are rare but powerful forms of intellectual property. They are usually reserved for product shape designs that have iconic characteristics. Their rarity suggests that the average company does not typically invest as much in product design as they should.
Here are some famous shape trademarks I have come across over the years.
Which one is your favorite? (Mine is the fish-shaped cracker)
Note: The product image is followed by the issued trademark.