Barium

ChemGlobe: Barium
Electronic, thermal, and steric data, along with an isotope table.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/56.html

ChemicalElements.com: Barium
Basic information, atomic structure, and isotopes.
http://www.chemicalelements.com/elements/ba.html

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

It's Elemental: Barium
Basic physical and historical information.
http://education.jlab.org/itselemental/ele056.html

LANL: Barium
History, sources, properties, and uses.
http://periodic.lanl.gov/elements/56.html

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

Visual Elements: Barium
Image, appearance, source, uses, key isotopes, and ionisation energies.
http://www.chemsoc.org/viselements/pages/barium.html

WebElements: Barium
Extensive information on history, uses, occurrence, compounds, and properties.
http://www.webelements.com/webelements/elements/text/Ba/key.html

Wikipedia: Barium
Properties of the element, including its history, applications, and characteristics.
http://en.wikipedia.org/wiki/Barium