ChemicalElements.com: Oxygen: Features basic information, an atomic structure diagram, facts about oxygen and a table of isotopes.
LANL: Oxygen: Details of the history, sources, forms, compounds, and isotopes of oxygen.
Visual Elements: Oxygen: Explains the uses and physical properties of oxygen. Includes a visual representation and downloadable animation.
WebElements: Oxygen: History, uses, occurrence, compounds, and properties. Features a picture of liquid oxygen and a sound file.
Wikipedia: Oxygen: Article covering properties of the element, including its history, applications, and characteristics as well as safety precautions.