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