Hafnium

EnvironmentalChemistry.com: Hafnium - Atomic structure, chemical and physical properties, and table of nuclides.
http://environmentalchemistry.com/yogi/periodic/Hf.html

It's Elemental: Hafnium - Basic physical and historical information.
http://education.jlab.org/itselemental/ele072.html

Lenntech: Hafnium - Physical data, chemical properties, health and environmental effects.
http://www.lenntech.com/Periodic-chart-elements/Hf-en.htm

WebElements: Hafnium - Extensive information on occurrence, compounds, and properties.
http://www.webelements.com/hafnium/

LANL: Hafnium - History, properties, uses, and handling.
http://periodic.lanl.gov/elements/72.html

Wikipedia: Hafnium - Properties of the element, including its history, applications, and characteristics.
http://en.wikipedia.org/wiki/Hafnium

ChemGlobe: Hafnium - Electronic, thermal, and steric data along with an isotope table.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/72.html

ChemicalElements.com: Hafnium - Basic information, atomic structure, and isotopes.
http://www.chemicalelements.com/elements/hf.html

Visual Elements: Hafnium - General and physical information, source, uses, key isotopes, and ionisation energies.
http://www.chemsoc.org/viselements/pages/hafnium.html