Geography World Games includes, among many more, National Geographic Geo Bee Challenge and discovery Channel Geo Game, as well as a link back to the Geography World homepage of related resources.
National Geographic Kids

 Parent & After-school Resources
ReadWriteThink

 StarChild Learning Center for Young Astronomers is a popular intereactive website with information about the solar system organized into appropriate reading levels for elementaty students.
StarChild

MightyBook features read-aloud picture books, sing-along songs, video song books, poetry, story-writing and illustrating contests and learning games designed for children ages 2-12.
Mightybook