Cementation.com

USGS Minerals Information: Selenium
Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
minerals.usgs.gov/

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

ChemGlobe: Selenium
Electronic, thermal, and steric data along with an isotope table.
partisans.spurious.biz/

LANL: Selenium
Production, properties, isotopes, and handling.
periodic.lanl.gov/

Lenntech: Selenium
Physical data, chemical properties, health and environmental effects.
www.lenntech.com/

WebElements: Selenium
Extensive information on history, uses, occurrence, compounds, and properties of the element.
www.webelements.com/

EnvironmentalChemistry.com: Selenium
Atomic structure, chemical and physical properties, and table of nuclides.
environmentalchemistry.com/

ChemicalElements.com: Selenium
Basic information, atomic structure, and isotopes.
www.chemicalelements.com/

It's Elemental: Selenium
Basic physical and historical information.
education.jlab.org/

Radiochemistry of Selenium
Full text of the monograph by V. J. Molinski (Union Carbide Corporation, Mining and Metals Division, Research Center, Tuxedo, New York) and G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
lib-www.lanl.gov/