Argon

ChemGlobe: Argon
Electronic, thermal, and steric data along with basic information.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/18.html

ChemicalElements.com: Argon
Basic information, atomic structure, and table of isotopes.
http://www.chemicalelements.com/elements/ar.html

EnvironmentalChemistry.com: Argon
Atomic structure, chemical and physical properties, and table of nuclides.
http://environmentalchemistry.com/yogi/periodic/Ar.html

Especiál Gas Inc.: Argon
Numeric data, uses, and general information.
http://www.c-f-c.com/specgas_products/argon.htm

It's Elemental: Argon
Basic physical and historical information.
http://education.jlab.org/itselemental/ele018.html

LANL: Argon
Sources, properties, isotopes, and uses.
http://periodic.lanl.gov/elements/18.html

Lenntech: Argon
Physical data, chemical properties, health and environmental effects.
http://www.lenntech.com/Periodic-chart-elements/Ar-en.htm

Visual Elements: Argon
General and physical information, uses, key isotopes, and ionisation energies.
http://www.chemsoc.org/viselements/pages/argon.html

WebElements: Argon
Extensive information on history, uses, occurrence, and properties of the element.
http://www.webelements.com/webelements/elements/text/Ar/key.html

Wikipedia: Argon
Details the properties of the element, including its history, applications, and characteristics.
http://en.wikipedia.org/wiki/Argon