In 1909, the Lincoln cent came into being, with the Wheat reverse. These were all copper, with the exception of the 1943 Steel Cent, which is actually not difficult to find in most conditions. The 1943 was produced in steel, because copper was allocated to the War effort. There are several key Wheat dates, including the 1909-S VDB, 1914-D, 1922 No D, 1931-S and a few others…. If you come across a 1943 Copper Cent, though, call me right away. These are extremely rare and valuable!!
The Lincoln Memorial reverse was introduced in 1959 with President Lincoln’s head remaining on the obverse. In 2009 several reverses were minted to commemorate Lincoln’s 200th birthday, and in 2010 the preservation of the Union was commemorated on the Lincoln’s reverse.
Lincoln Cents are arguably the most collected US type coin, although Flying Eagle-Indian Head collectors may be considered their specialty to be more interesting.