Astronomy

Oulu Space Physics Textbook: From the Space Physics Group, Oulu, Finland. Information about the Sun, the solar wind, the magnetosphere, ionosphere, auroras, cosmic rays, and more.
Astronomy Notes: A very complete and thorough introduction to astronomy. Covers a wide range of topics.
Educational Guide to Space and Astronomy: A great place to learn more about astronomy amd space missions.
The Talk.Origins Archive: An archive exploring the origins of life, radiometric dating, the controversy between creation and evolution, and many other interesting and related topics.
Bad Science: This site focuses on certain topics and/or concepts in science that are often difficult to understand, not just for students learning new material, but also for teachers teaching it as well.
Science at Nasa: The latest science news on a variety of topics from NASA
Science World: Eric Wiesstein's World of Science at Wolfram Research. The topics covered include astromomy, physics, scientific biography, mathematics, and chemistry.
An Atlas of the Universe: A collection of maps, allowing you to zoom in and/or zoom out while viewing maps of the Sun and its surroundings.
SEDS: Students for the Exploration and Development of Space. Discussion forum, images of space, sky maps, and links to other related resources.
Astronomy Picture of the Day: Each day, a different picture of some part of the universe is presented, along with a brief explanation.