The Weather Channel
Web companion to the popular U.S.-based cable television network that provides current conditions and forecasts for over 1,700 cities worldwide (including 3-5 day forecasts), along with local and regional radars. Many maps and other features are at one's fingertips plus weather-related news, educational material, a weather glossary, a storm encyclopedia and seasonal features.
The Weather Underground
A good companion resource to The Weather Channel, with its own unique offerings beyond the required fare. Now the most widely translated weather site in the world, with over 35 languages, Weather Underground features include historical weather conditions and astronomy.