• Rates for Domestic Letters, 1863-2008 (pdf) (rtf)
• Rates for Domestic Letters, 1792-1863 (pdf) (rtf)
• Rates for Stamped Cards and Postcards, 1873-2008 (pdf) (rtf)
• Pieces of Mail Handled, Number of Post Offices, Income, and Expenses, 1789 to 2008 (pdf) (htm)
• Delivery Points, 1990 to 2008, in Millions (pdf) (htm)

More historical statistics are available in Historical Statistics of the United States, Colonial Times to 1970, and the annual Statistical Abstract of the United States, from the U.S. Census Bureau. The Statistical Abstract, first available for 1878, offers expanded coverage of the Postal Service beginning in 1909.

The Bureau of Labor Statistics' CPI inflation calculator calculates the current values of past prices back to 1913. You can compare values back to 1774 at www.measuringworth.com.