This program looks at the historical data file from bitcoinwatch.com, and reports the high, low, and average price of each currency, in bitcoins, for a given year/month/day/whatever. See the README for details.
The main page is here:https://savannah.nongnu.org/projects/btctrade
The direct download is here:http://download.savannah.gnu.org/releases/btctrade/btctrade-0.2.0.tar.bz2
I gladly accept bug reports, donations, and feature requests. I warn you though, that I use a GNU operating system, so I'm not 100% sure how it will work on Windows or Mac.
EDITED to reflect current version.