Strontium

ChemGlobe: Strontium - Electronic, thermal, and steric data along with an isotope table.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/38.html

LANL: Strontium - History, forms, properties, isotopes, and uses.
http://periodic.lanl.gov/elements/38.html

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

Visual Elements: Strontium - Uses, physical information, key isotopes, and ionisation energies.
http://www.chemsoc.org/viselements/pages/strontium.html

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

ChemicalElements.com: Strontium - Basic information, atomic structure, and isotopes.
http://www.chemicalelements.com/elements/sr.html

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

It's Elemental: Strontium - Basic physical and historical information.
http://education.jlab.org/itselemental/ele038.html

USGS Minerals Information: Strontium - Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
http://minerals.usgs.gov/minerals/pubs/commodity/strontium/

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