Once in a while, someone has a great idea that becomes a fad, a product that is immensely popular for a short time. Some fads have gone on to be classics; others have just gone. Anyone can have an idea that becomes a fad, and fads usually make their originators rich.

Silly Putty (1944)

Chemists at General Electric working with silicone stumbled across this material that can be kneaded, bounced, and stretched. In 1949, Peter Hodgson thought it would make a great toy. After an investment of $150, Hodgson sold 1-ounce bags of putty in plastic eggs. It was an instant success. Millions of eggs of Silly Putty have been sold and continue to sell to this day.

Slinky (1945)

When he was 26, Richard James of Philadelphia invented the Slinky. It consists of 87 feet of flat wire coiled into 3-inch-diameter circles and stands about 2 inches high when stacked. The Slinky's ability to “walk” down stairs and open and close like an accordion made it a favorite toy during the 1950s, and it is still popular today.

Hula Hoop (1958)

Arthur Melin and Richard Knerr, founders of the Wham-O Toy Company, took an idea from Australia, where gym students exercised using bamboo hoops, and turned it into the biggest fad of all time. The Hula Hoop is a round plastic tube that can be rotated around the waist by swinging the hips. It can also be jumped through, used as a jump rope, or spun around the neck. More than 25 million had been sold only four months after it was introduced.

Mood Rings (1975)

Mood rings were made of heat-sensitive liquid crystals encased in quartz. When the body temperature of the wearer changed, the crystals changed color, supposedly indicating how the wearer felt at the moment. Blue meant happy; reddish brown meant insecure; green meant active; black meant the wearer was tense and upset. Joshua Reynolds, a 33-year-old New Yorker, created and marketed the original mood ring.

Pet Rocks (1975)

More than a million people bought Pet Rocks as Christmas gifts in 1975. Gary Dahl, of Los Gatos, California, had the idea while joking with friends about his easy-to-care-for pet, a rock. This pet ate nothing and didn't bark or chew the furniture. Pet Rocks were sold with a funny manual that included tips on how to handle an excited rock and how to teach it tricks. By 1976, Gary Dahl was a millionaire and Pet Rocks were the nation's favorite pet.

Rubik's Cube (1977)

Hungarian architect Erno Rubik designed geometric models in his spare time and came up with a cube, with each face consisting of nine smaller cubes. He used it to teach algebraic group theory, but a Hungarian trading company saw its potential as a puzzle toy and began marketing it. By 1980, more than 100 million Rubik's Cubes had been sold around the world, as well as another 50 million “knock-off” cubes not authorized by Rubik. The Cube led to a mini-industry with some 50 books published explaining how to solve the puzzle. Though its popularity has declined, one can still purchase Rubik's Cube at toy stores today.

Furby (1998)

Furby was an electronic furry robot. It resembled a cross between an owl and a hamster and was a must-have during the 1998 holiday season. By 1999, 14 million had sold. Furby was created by Dave Hampton and Caleb Chung. They spent nine months creating Furby.