Yttrium

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

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

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

WebElements: Yttrium
Extensive information on history, uses, occurrence, compounds, and properties of the element.
http://www.webelements.com/webelements/elements/text/Y/key.html

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