As of 2009, it costs the government 1.62 cents to produce a copper plated zinc penny (up from .008 cents in 2001), 6.03 cents to produce a nickel, 5.65 cents to produce a dime, 11.31 cents to produce a quarter, 30.4 cents to make the 'gold' (manganese/brass)dollar, and 6.4 cents to make a dollar bill.
In 2008 a bill was introduced known as the Coin Modernization and Taxpayer Savings Act of 2008. This bill had proposed changing the composition of the cent to steel, although it would be treated to impart a copper color. The bill would have also provided the Secretary of the Treasury with authority to change the metallic content of the five cent coin. This bill was passed in the House, but never voted on in the Senate.
The 2011 Budget revives the issue and expands the scope to include the dime, quarter, and half dollar, in addition to the penny and nickel. The Department of the Treasury will have authorization to approve alternative weights and compositions for any of these five denominations. It hasn't passed yet, but a penny saved. . .