Environmental Chemistry
Environmental chemistry.com: Periodic Table Oxygen
An incredibly thorough site with a wealth of basic information on oxygen. Highly recommended.
Chem4kids
Chem4 Kids: Oxygen (O)
Here you can find some great information about the 8th element in the periodic table, "oxygen." Content focuses on oxygen's electrons, where you can find oxygen in nature and in the home, and how oxygen combines with other elements.