The Old Farmer's Almanac
This site contains weather information and historical weather data for any location in the United States or Canada, 1973-present.
National Oceanic And Atmospheric Administration (NOAA)
The NOAA National Weather Service is the primary source for all weather data, forecasts and warnings for the United States. It is the official voice for the U.S. when it comes to issuing warnings during life-threatening weather situations. The weather data issued by NOAA's National Weather Service is free and in the public domain. There is also an archive containing 108 years of weather data for the United States.
This site contains Vaisala Lightning Explorer®, a free U.S. lightning map. It tracks recent thunderstorm movement and lightning activity on a map of the continental U.S using your web browser. Note that activity is delayed by 30 minutes.
National Climatic Data Center
This site contains an archive of climatic data - much of it is free. As of the time of this writing, the free data includes an extreme weather and climate events database, climate monitoring reports and products, a U.S. storm events database, and so much more!
U.S. Road Conditions
This site contains updated road conditions, traffic reports and a live look at highway weather conditions.
The Weather Hub
This site has links for over 1500 U.S. cities - historical weather data is included!
This site has collected comprehensive weather information for 16,439 cities worldwide.
The Weather Underground
Find the weather for any city, state, zip code, airport code, or PDA mobile. Get the results in English, metric or both.
This site provides a complete source of graphical weather information. They also provide an archive of satellite images, surface maps and upper air data that goes back a couple of months.
FAQ: Finding Data On Past Weather
Here is an interesting article dated October 27, 2003, at USA Today by Jack Williams that discusses how to find specific kinds of weather records.
These sites have current weather information and historical data. Historical data can, for example, be useful when one is conducting an investigation of accidents when one needs to know what road and weather conditions were like on a specific date.
Know of a site that belongs on this list? Contact Spies Online.