Britannica Nobel Prize: Astatine
   Overview and basic data.
   http://www.britannica.com/nobel/micro/38_12.html

ChemGlobe: Astatine
   Electronic, thermal, and steric data, along with a table of isotopes.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/85.html

Chemical Elements.com: Astatine
   Basic information, atomic structure, and table of isotopes.
   http://www.chemicalelements.com/elements/at.html

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

It's Elemental: Astatine
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele085.html

LANL: Astatine
   History, uses, production, and properties.
   http://periodic.lanl.gov/elements/85.html

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

Radiochemistry of Astatine
   Full text of the monograph by Evan H. Appelman (Argonne National Laboratory, Lemont, Illinois). [PDF]
   http://lib-www.lanl.gov/cgi-bin/getfile?rc000018.pdf

Visual Elements: Astatine
   General and physical information, source, key isotopes, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/astatine.html

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