Today's pennies (since 1983) are made almost entirely of zinc, with a thin outer coating of copper.
Information corrected based on PCGS data, and merged 02/2009
- Large cents (1793-1857) : 100% copper
- Flying Eagle and early Indian cents (1857-mid 1864) : 87.5% copper, 12.5% nickel, also known as NS-12
- Indian head and Lincoln cents (mid-1864 to 1942 and 1946-61 : bronze (95% copper, 5% tin and zinc)
- Lincoln cents (1943) : 1943 zinc-coated steel due to wartime copper shortages. (Note: These are sometimes called "silver" or "lead" cents by people who aren't aware they're really steel.)
- Lincoln cents (1944-46, 1961-mid 1982) : brass (95% copper, 5% zinc)
Actually, modern pennies(post 1982) are 97.5% Zinc with the remaining 2.5% being electrolytically plated copper. Up till 1982, pennies were made from and alloy composed of 95% Copper, 2-3% Zinc and 2-3% Tin.
Additionally, the 1943 "wartime penny" or the "steel penny" was made of steel with zinc plating, so that copper could be saved for military use. A few of these pennies were accidentally minted early in 1943 with bronze blanks left over from 1942, and are prized by collectors.