ChemGlobe: Platinum
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/78.html

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

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

It's Elemental: Platinum
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele078.html

LANL: Platinum
   Sources, properties, and uses.
   http://periodic.lanl.gov/elements/78.html

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

Radiochemistry of Platinum
   Full text of the monograph by G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
   http://lib-www.lanl.gov/cgi-bin/getfile?rc000037.pdf

Visual Elements: Platinum
   Image, general and physical information, source, uses, key isotopes, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/platinum.html

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