I came across this and thought it would be fun for you Americans to see!

Since July 1, 1863, letters sent to all parts of the United States have been charged at the same rate.

July 1, 1863 3 cents per 1/2 oz.
Oct. 1, 1883 2 cents per 1/2 oz.
July 1, 1885 2 cents per 1 oz.
Nov. 2, 1917 3 cents per 1 oz.*
July 1, 1919 2 cents per 1 oz.
July 6, 1932 3 cents per 1 oz.
Aug. 1, 1958 4 cents per 1 oz.
Jan. 7, 1963 5 cents per 1 oz.
Jan. 7, 1968 6 cents per 1 oz.
May 16, 1971 8 cents per 1 oz.
March 2, 1974 10 cents per 1 oz.
Dec. 31, 1975 13 cents for 1st oz.**
May 29, 1978 15 cents for 1st oz.
March 22, 1981 18 cents for 1st oz.
Nov. 1, 1981 20 cents for 1st oz.
Feb. 17, 1985 22 cents for 1st oz.
April 3, 1988 25 cents for 1st oz.
Feb. 3, 1991 29 cents for 1st oz.
Jan. 1, 1995 32 cents for 1st oz.
Jan. 10, 1999 33 cents for 1st oz.
Jan. 7, 2001 34 cents for 1st oz.
June 30, 2002 37 cents for 1st oz.