Neptunium

ChemGlobe: Neptunium
Electronic, thermal, and steric data along with an isotope table.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/93.html

ChemicalElements.com: Neptunium
Basic information, atomic structure, and isotopes table.
http://www.chemicalelements.com/elements/np.html

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

It's Elemental: Neptunium
Basic physical and historical information.
http://education.jlab.org/itselemental/ele093.html

LANL: Neptunium
Basic information and history.
http://periodic.lanl.gov/elements/93.html

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

Visual Elements: Neptunium
General and physical information, source, and key isotopes.
http://www.chemsoc.org/viselements/pages/neptunium.html

WebElements: Neptunium
Extensive information on history, uses, compounds, and properties.
http://www.webelements.com/webelements/elements/text/Np/key.html

Wikipedia: Neptunium
Notable characteristics, history, occurrence, isotopes, and weapons applications.
http://en.wikipedia.org/wiki/Neptunium