BBC: The Seasons: Find out why the seasons change.
New Science: A Change of Season: From NASA, a discussion of solstice and equinox. Includes animations explaining why the seasons happen.
NWS Winter Weather Awareness: Lists information about how to handle winter weather situations.
Seasons of the Year: First grade web quest on the seasons of the year.
The Electronic Passport to Seasons: A basic description of seasons with a diagram.
The Four Seasons: Includes games, coloring pages, crafts, and stationery for each of the four seasons. From PrimaryGames.com
The Seasons: A description of the seasons, and common misconceptions about what causes them.
Why Leaves Change Color: From the SUNY College of Environmental Science and Forestry, an article explaining what happens when leaves change colors in the Fall.
Wildlife Garden - Seasons: From the Museum of Natural History, a daily photographic record showing how the Museum's wildlife garden changes over the course of a year.
Winter Storms: Try out Scholastic's Interactive Weather Maker and learn how the wind chill factor works.