Steel pennies were used during WWII to conserve copper. Some 1943 copper pennies were mistakenly manufactured, making them unusual and valuable.
A double die error caused a tiny number of 1955 pennies to have the design stamped twice. Collectors adore these coins.
Pre-1965 dimes were 90% silver. Silver makes pre-1965 Roosevelt dimes worth more than their face value.
Washington quarters manufactured before 1965 are 90% silver and worth more than their face value, like Roosevelt dime.
Kennedy half dollars from 1964 are 90% silver. They're rare and expensive.
Nickels manufactured from 1942 to 1945 include 35% silver because they were needed during WWII. Silver content makes these desirable to collectors.
Some 2004 Wisconsin state quarters had an extra leaf on the ear of corn on the back. Mistake coins might be worth much more than their face value.