The English/British One Penny coin has been issued for over 1,100 years.
All years of issue of the British decimal New Penny and Penny are still potentially in circulation so, unless they are part of a Proof or uncirculated mint set or are individual Proof or uncirculated coins and in absolute mint condition, they are worth 1 Penny.
20th century predecimal Pennies would need to be in mint condition to attract any significant value.
The most spectacularly valuable example would be the 1933 Penny. There are 7 known coins.
Other than that, there would be the -
1919 (KN mintmark & H mintmark),
1918 (KN mintmark & H mintmark),
1909 (variant - 1 directly above tooth)
1902 (variant - with low tide - further done Britannia's shin)
The Queen Victoria, penny-red, plate 77, one penny stamp.
As far as general circulation coins are concerned, easily the most valuable Australian Penny is the 1930 Penny and the most valuable Halfpenny would be the 1923 Halfpenny.
On the 1969 S penny a doubling of the print makes it very valuable ($35 000)
Penny
This is an uncommon error and one example was estimated to be worth excess of $20,000.
about 0.3 oz
What mainly determines the value is the rarity of the penny. A date where 3 billion were minted is never going to be worth as much as one with under 1 million.
Nothing
1937 penny
1794/5 Flowing hair silver/copper dollar
Generally, coins are valuable because of the price of the metals they are made from, but if you mean in a collectible way: One thing that makes a penny valuable is the date. They older the coin usually the more valuable. Another thing is the mintmark. For example 1943 pennies with a "S" mintmark are more valuable than pennies with no mintmark. Another thing is the condition of the coin. The less ware it has the more it's worth.
any copper penny is worth more than its face value.