Hafnium
Links
It's Elemental: Hafnium
http://education.jlab.org/itselemental/ele072.html
Basic physical and historical information.
ChemicalElements.com: Hafnium
http://www.chemicalelements.com/elements/hf.html
Basic information, atomic structure, and isotopes.
Visual Elements: Hafnium
http://www.chemsoc.org/viselements/pages/hafnium.html
General and physical information, source, uses, key isotopes, and ionisation energies.
Wikipedia: Hafnium
http://www.wikipedia.org/wiki/Hafnium
Properties of the element, including its history, applications, and charateristics.
EnvironmentalChemistry.com: Hafnium
http://environmentalchemistry.com/yogi/periodic/Hf.html
Atomic structure, chemical and physical properties, and table of nuclides.
WebElements: Hafnium
http://www.webelements.com/webelements/elements/text/Hf/key.html
Extensive information on history, uses, occurrence, compounds, and properties.
Lenntech: Hafnium
http://www.lenntech.com/Periodic-chart-elements/Hf-en.htm
Physical data, chemical properties, health and environmental effects.