Neptunium
Links
ChemicalElements.com: Neptunium
http://www.chemicalelements.com/elements/np.html
Basic information, atomic structure, and isotopes table.
It's Elemental: Neptunium
http://education.jlab.org/itselemental/ele093.html
Basic physical and historical information.
Neptunium
http://www.scescape.net/~woods/elements/neptunium.html
Data tables and historic information.
Visual Elements: Neptunium
http://www.chemsoc.org/viselements/pages/neptunium.html
General and physical information, source, and key isotopes.
EnvironmentalChemistry.com: Neptunium
http://environmentalchemistry.com/yogi/periodic/Np.html
Atomic structure, chemical and physical properties, and table of nuclides.
WebElements: Neptunium
http://www.webelements.com/webelements/elements/text/Np/key.html
Extensive information on history, uses, compounds, and properties.
Lenntech: Neptunium
http://www.lenntech.com/Periodic-chart-elements/Np-en.htm
Physical data, chemical properties, health and environmental effects.
Wikipedia: Neptunium
http://en.wikipedia.org/wiki/Neptunium
Notable characteristics, history, occurrence, isotopes, and weapons applications.