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

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

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

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

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

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

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/

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

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