ChemGlobe: Platinum - Electronic, thermal, and steric data along with an isotope table. - http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/78.html
LANL: Platinum - Sources, properties, and uses. - http://periodic.lanl.gov/elements/78.html
Wikipedia: Platinum - Properties of the element, including its history, applications, and characteristics. - http://en.wikipedia.org/wiki/Platinum
Lenntech: Platinum - Physical data, chemical properties, health and environmental effects. - http://www.lenntech.com/Periodic-chart-elements/Pt-en.htm
EnvironmentalChemistry.com: Platinum - Atomic structure, chemical and physical properties, and table of nuclides. - http://environmentalchemistry.com/yogi/periodic/Pt.html
Visual Elements: Platinum - Image, general and physical information, source, uses, key isotopes, and ionisation energies. - http://www.chemsoc.org/viselements/pages/platinum.html
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