Calcium: Data tables and historic information.
ChemGlobe: Calcium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Calcium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Calcium: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Calcium: Basic physical and historical information.
LANL: Calcium: History, sources, properties, uses, and compounds.
Lenntech: Calcium: Physical data, chemical properties, and health effects.
Visual Elements: Calcium: Image, animation, source, uses, and physical information.
WebElements: Calcium: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Calcium: Properties of the element, including its history, applications, and characteristics.