ChemGlobe: Promethium
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/61.html

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

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

It's Elemental: Promethium
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele061.html

LANL: Promethium
   History, sources, uses, and properties.
   http://periodic.lanl.gov/elements/61.html

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

Visual Elements: Promethium
   Image, animation, source, uses, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/promethium.html

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