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