eNature: America's Wildlife Resource
Gives photos and facts about the breeding, habitat, and range of over 4,800 North American plants and animals, courtesy of the National Audubon Society Field series.
Human Anatomy Online
Provides quality information about the human body. Includes ten clickable images, representing body systems. Grades 7 up.
Mad Sci Network
Offers free "Ask-An-Expert" service staffed by volunteer scientists, plus a large archive of answered questions.
Rose Center for Earth and Space
Provides virtual tours, activities and resources, and a weekly space watch.
Sea and Sky
Provides information about astronomy and oceanography, featuring image galleries, games, articles, and links to other similar resources on the web.
Offers a science current-events service, covering a wide range of stories from fossils to floods to flu. Archives are conveniently sorted by field.