NASA for middle-school students http://www.nasa.gov/audience/forstudents/5-8/features/index.html
National Geographic for Kids http://www.nationalgeographic.com/kids/
Science News http://sciencebulletins.amnh.org/; http://www.sciencenewsforkids.org/; http://www.nsta.org/sciencenews
Chemistry Help http://chem4kids.com
Earth Science http://earthsky.com; http://www.fi.edu/tfi/hotlists/geology.html; http://www.earthsciweek.org; http://usgs.gov
Great Science Links http://sciencespot.net/Pages/kidzone.html