ChemGlobe: Yttrium
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/39.html

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

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

It's Elemental: Yttrium
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele039.html

LANL: Yttrium
   History, sources, properties, uses, and isotopes.
   http://periodic.lanl.gov/elements/39.html

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

The Columbia Encyclopedia: Yttrium
   Overview for the general reader.
   http://www.bartleby.com/65/yt/yttrium.html

Visual Elements: Yttrium
   Image, animation, uses, physical information, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/yttrium.html

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