What is the most expensive penny?
If you're referring to a US cent, the record holder as of
09/2011 is a 1943-D cent accidentally struck in bronze. In MS-64
condition it sold for somewhat under $2 million.
If you're referring to British pennies, there are several
possible candidates but the 1933 1d coin is probably the most
famous. Only 1 was struck and it is considered to be priceless.