Science Struck
Science Struck: The Four Main Layers of the Earth
Gives short descriptions of the crust, mantle, outer core, and inner core.
Science4Fun
Science4 Fun: Composition of the Earth
Provides a discussion of the layers of the earth including the crust, mantle, inner core, and outer core.
Other
Moorland School: Earth Science Zone: The Structure of the Earth
Take a look at the Earth from the inside out. This site shows the different layers of the earth with an explanation of the rocks and materials in each layer. Includes a quiz on the structure of Earth.
Treehut
Suzy's World: Earth
At this site from Suzy's World and Suzy Cato, you can find out what the earth is made of and try an experiment.