US Geological Survey
Usgs: Inside the Earth
This is a website to learn not only about the inner and outer core, but also about the crust and the mantle of the interior of the earth.
Rice University
Museums Teaching Planet Earth: What Is the Geosphere?
Describes Earth's layers, which make up the geosphere.
CK-12 Foundation
Ck 12: Earth Science: Earth's Interior Study Guide
This comprehensive study guide covers the main terms and concepts needed for an earth science unit on the earth's interior. Review questions are included at the bottom of the study guide.