ChemGlobe: Iron: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Iron: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Iron: Atomic structure, chemical and physical properties, and table of nuclides.
Iron: Data tables and historic information.
It's Elemental: Iron: Basic physical and historical information.
LANL: Iron: History, sources, uses, and properties.
Lenntech: Iron: Physical data, chemical properties, health and environmental effects.
Radiochemistry of Iron: Full text of the monograph by J. M. Nielsen (Hanford Laboratories, Hanford Atomic Products Operation, Richland, Washington). [PDF]
USGS Minerals Information: Iron: Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
Visual Elements: Iron: Image, general and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Iron: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Iron: Properties of the element, including its history, applications, and characteristics.