http://oregonstate.edu/instruct/anth484/minwage.html

A federal minimum wage was first set in 1938. The graph shows nominal (blue diamonds) and real (red squares) minimum wage values. Nominal values range from $0.25/hr in 1938 to the current $5.15/hr. The graph adjusts these wages to 2006 dollars (red squares) to show the real value of the minimum wage. Calculated in real 2006 dollars, the 1968 minimum wage was the highest at $9.27. The real dollar minimum wage (red squares) rises and falls because of periodic adjustments by Congress. The period 1997-2007, is the longest period during which the minimum wage has not been adjusted. The House, January 10, 2007, voted a minimum wage increase to $5.85, to take effect 60 days after the measure becomes law. The green triangles show the real minimum wage increase in 2006 dollars for the three increments $5.85, $6.85 one year after becoming law (i.e., 2008, assuming the minimum wage increases in 2007) and $7.25 after two years (2009). The real values after 2006 are projected for future decline in purchasing power if the minimum wager is not raised. Many states have departed from the federal minimum wage. Washington has the highest minimum wage in the country at $7.93 as of January 1, 2007.