A Cheerios Penny
is a year 2000 Lincoln Memorial penny that was put into a Cheerios cereal box for a special promotion in early 2000. The U.S. Mint provided 10,000,000 freshly-struck pennies, plus 5,500 brand new Sacagawea Dollars to General Mills, who placed them onto plastic-sealed cards (see photo) which then went into cereal boxes. Although the vast majority of the cards had one coin on them, (the penny,) 5,500 of the cards had two coins, the penny and a Sacagawea Dollar. The point of the promotion was to help raise awareness about the then-new Sacagawea "Golden Dollars."
The reason these coins are noteworthy today is that the so-called Cheerios Dollars were struck from different dies than normal Sacagawea Dollars, making them a very rare variety. Although Cheerios Pennies are generally nothing special, a small percentage have been found to have come from dies meant for Proof pennies, and they have the "Wide AM" reverse die type. The average Cheerios Penny which is still on its card is worth about $5 on eBay. (A 2000 Lincoln Cent that is not on the sealed Cheerios card is only worth face value.)
See also: Cheerios Dollars
More information about the "Wide AM" variety coin can be found on the list of top 10 most valuable coins found in pocket change
The Cheerios Penny
is one of the more unusual cereal-box prizes in recent memory, and probably would have been forgotten had the Cheerios Dollars not been discovered to be so rare.