How much has the cost of living gone up compared to our buying power over the past 20 years?

Answer 1

Here you go, a nice chart back to 1950
http://www.investmenttools.com/thestate/rate_of_inflation_yearly.htm

And another chart
http://www.econedlink.org/lessons/index.cfm?lesson=EM222

Here is inflation data since 2000.
http://inflationdata.com/inflation/inflation_rate/CurrentInflation.asp

And the CPI data for the past 10 years
http://inflationdata.com/Inflation/Consumer_Price_Index/HistoricalCPI.aspx

Here is inflation rates by decade
http://inflationdata.com/Inflation/Inflation_Rate/DecadeInflation.asp

Formula for calculating inflation
http://inflationdata.com/Inflation/Articles/CalculateInflation.asp