I use Weather Underground:
http://www.wunderground.com/global/stations/12375.html
if you scroll down, you will find the 'almanac' section, which is really useful for matching historical weather with the date in question.
"Good luck, you're on your own - and the weather at 6:00am on July 18, 2000, is scattered clouds with a 10-knot wind from the west..."