ChemGlobe: Zirconium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Zirconium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Zirconium: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Zirconium: Basic physical and historical information.
LANL: Zirconium: History, isotopes, properties, and uses.
Lenntech: Zirconium: Physical data, chemical properties, health and environmental effects.
USGS Minerals Information: Zirconium: Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
Visual Elements: Zirconium: Image, uses, physical information, and ionisation energies.
WebElements: Zirconium: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Zirconium: Properties of the element, including its history, applications, and characteristics.
Zirconium: Data tables and historic information.