Barium

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

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

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

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

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

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

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

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