ChemGlobe: Germanium: Electronic, thermal, and steric data along with an isotope table.
ChemicalElements.com: Germanium: Basic information, atomic structure, and isotopes.
Discovery of Germanium: Article by Clemens Winkler.
EnvironmentalChemistry.com: Germanium: Atomic structure, chemical and physical properties, and table of nuclides.
Germanium: Data tables and historic information.
It's Elemental: Germanium: Basic physical and historical information.
LANL: Germanium: History, sources, uses, and properties.
Lenntech: Germanium: Physical data, chemical properties, health and environmental effects.
Radiochemistry of Germanium: Full text of the monograph by Jacob A. Marinsky (University of Buffalo, Dept. of Chemistry, Buffalo, New York). [PDF]
USGS Minerals Information: Germanium: Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
WebElements: Germanium: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Germanium: Properties of the element, including its history, applications, and characteristics.