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