The inflation calculator:
http://www.westegg.com/inflation/
Some links from there:
17th Century Prices and Wages:
http://www.portsdown.demon.co.uk/mark.htm
Current value of old money (EXCELLENT links from this site [some below]):
http://www.ex.ac.uk/~RDavies/arian/current/howmuch.html
How much is that worth today?
http://www.eh.net/ehresources/howmuch/dollarq.php
The Purchasing Power of Money (paper and coin) during the Revolutionary War:
http://www.coins.nd.edu/ColCoin/FAQ/revolutval.html
Pennsylvania Currency 1756-1789:
http://www.coins.nd.edu/ColCurrency/CurrencyText/PA.html
[Includes pictures of currency!]
Above site taken from the page Colonial Currency (links to different states)
(interesting essays at the bottom of this site as well):
http://www.coins.nd.edu/ColCurrency/index.html
Commodity: Money
[Very interesting site. For example: in 1635 a law was passed that full
bore musket balls would be allowed to pass as farthings, but no one was
required to accept more than 12 pence worth at a time (as there were four
farthings to a penny, this would be 48 balls).]
http://www.coins.nd.edu/ColCoin/ColCoinIntros/Commodity.intro.html