US Naval Observatory Data Services: calculates times of astronomical events for any given day & location
Observing the Heavens Above!
Award winning daily science radio series with a variety of articles, teacher resources, kids stuff, etc.
Phil Harrington's StarWare, advice and information page for amateur astronomers
Astronomy 101 portal: for high quality resources of images, activities, news, notes, etc...
NASA's StarChild site: for young (and old) astronomers.