ChemGlobe: Mercury: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Mercury: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Mercury : Nuclides: Extensive information on the nuclides of mercury, including potential parent nuclides.
It's Elemental: Mercury: Basic physical and historical information.
LANL: Mercury: Basic information, history, and uses.
Lenntech: Mercury: Physical data, chemical properties, health and environmental effects.
Mercury: Data tables and historic information.
Mercury: A very brief description of Mercury, with a good diagram of its electron orbitals.
Mercury and Methylmercury by IC-ICPMS: Analysis of biological, pharmaceutical, and environmental samples for methylmercury and mercury.
Mercury in Space: Answers the question of what happens to Mercury in space.
Mercury in the Laboratory: Practical considerations when working with mercury in the laboratory.
Mercury, Get Mad Now, Not Later: Gives a description of mercury, as well as its uses and environmental and health hazards associated with it.
Radiochemistry of Mercury: Full text of the monograph by Josef Roesmer (Westinghouse Astronuclear Laboratory, Pittsburgh, Pennsylvania). [PDF]
Sandia National Laboratories : Mercury: Information about mass of isotopes of mercury. Also information on analyzing it, such as Heavy Ion BackScattering and Rutherford BackScattering.
USGS Minerals Information: Mercury: Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
Vermont Legislative Research Shop - Mercury Information: Features basic information about Mercury, as well as its harmful effects and legislation concerning Mercury in some American States.
Visual Elements: Mercury: Image, general and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Mercury: Contains extensive information about Mercury, as well as pictures and videos that show its physical appearance and how it reacts with certain chemicals.
Why is Mercury liquid at room temperature?: Explores the question of why Mercury is liquid at room temperature. It also provides some links to other sites regarding this chemistry quandary.
Why Worry About Mercury : Chemical Properties: Gives some chemical properties of mercury, as well as hazard precautions when dealing with mercury.
Wikipedia: Mercury: Properties of the element, including its history, applications, and characteristics.