ChemGlobe: Sulfur: Electronic, thermal, and steric data along with basic information.
ChemicalElements.com: Sulfur: Basic information, atomic structure, and table of isotopes.
EnvironmentalChemistry.com: Sulfur: Atomic structure, chemical and physical properties, and table of nuclides.
It's Elemental: Sulfur: Basic physical and historical information.
LANL: Sulfur: History, properties, production, and uses.
Lenntech: Sulfur: Physical data, chemical properties, health and environmental effects.
Radiochemistry of Sulfur: Full text of the monograph by G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
Sulfur: Data tables and historic information.
Sulphur versus Sulfur: Some thoughts on the history of the spelling of the name of element 16: 'sulfur' vs 'sulphur'.
USGS Minerals Information: Sulfur: Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
Visual Elements: Sulfur: Image, general and physical information, source, uses, key isotopes, and ionisation energies.
WebElements: Sulfur: Extensive information on history, uses, occurrence, compounds, and properties of the element.
Wikipedia: Sulfur: Properties of the element, including its history, applications, and characteristics.