ChemGlobe: Manganese
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/25.html

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

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

It's Elemental: Manganese
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele025.html

LANL: Manganese
   Sources, properties, uses, and handling.
   http://periodic.lanl.gov/elements/25.html

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

Radiochemistry of Manganese
   Full text of the monograph by R. P. Schuman (Dept. of Chemistry, Robert College, Bebek P.K.8, Istanbul, Turkey). [PDF]
   http://lib-www.lanl.gov/cgi-bin/getfile?rc000060.pdf

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

Visual Elements: Manganese
   General and physical information, source, uses, biological role, key isotopes, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/manganese.html

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