Reply #29: I don't know if there's a definitive "formula"...

[tuvor]

But I use an application on my Palm called InflationMaster. "InflationMaster uses actual inflation data published by the United States Federal Reserve and takes into account years with high inflation, years with low inflation even deflationary years."

I googled around a bit for you, and found this, which suggests that this application might be using the Consumer Price Index to come up with its results. However, there are other methods, too:

Six Ways to Compute the Relative Value of a U.S. Dollar Amount, 1790 - 2007
http://www.measuringworth.com/uscompare/