NASA
Nasa: Earth: Overview: Our Home Planet
Provides a comprehensive look at the planet Earth including photos, how Earth got its name, and facts and figures about its size, seasons, moon, atmosphere, rotation, and lithosphere.
Smithsonian Institution
Smithsonian Education: Ocean Planet
A series of lesson plans designed to be used with the Smithsonian Ocean Planet exhibit (available online). Lesson topics include marine ecosystems, pollution of ocean water, animal strandings, and literature.