The National Oceanic and Atmospheric Administration (NOAA) http://www.noaa.gov
This web site is the launching off point to weather and climate information on the Internet.
The National Climatic Data Center (NCDC) http://www.ncdc.noaa.gov/oa/ncdc.html
The NCDC is part of the larger NOAA site but NCDC focuses on being the world's largest archive of climatic data.
In addition, resources for younger researchers are included in the selection of web sites presented in the Kids Stuff module. A variety of exercises, quizzes, podcasts, etc., are provided for use with students.