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