ChemGlobe: Gadolinium
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/64.html

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

Corrosionsource.com: Gadolinium
   History, occurrence, properties, isotopes, and uses.
   http://www.corrosionsource.com/handbook/periodic/64.htm

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

It's Elemental: Gadolinium
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele064.html

LANL: Gadolinium
   History, sources, properties, and uses.
   http://periodic.lanl.gov/elements/64.html

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

Visual Elements: Gadolinium
   Image, source, uses, physical information, and key isotopes.
   http://www.chemsoc.org/viselements/pages/gadolinium.html

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