Google Calculator can convert one currency to another at today's exchange rates, but often I'll want to convert one currency to itself at a different time. For example, what would $1,000 in 1930 be worth in today's dollars? Is there a Web app to do this?
Slap it into WolframAlpha (although I still dislike the guess-the-syntax game)
Here is what you can use.
compute the current value of a historical quantity of money
compute historical equivalent value of today's money
convert one historical quantity of money to another
$ 12952.10(2010 US dollars)
Also gives the purchasing power.
Try this site, it gives the purchasing power of money for the US and UK going back to 1257 http://eh.net/hmit/
You have to apply an inflation based coefficient, there's an entire site on this topic: http://inflationdata.com/Inflation/Inflation/Inflation.asp.
However it is not that simple, as the raw convertion is not an indication of the real value of money. So you have to take in account purchasing power: http://www.measuringworth.com/ppowerus/