ChemGlobe: Americium - Electronic, thermal, and steric data along with an isotope table. - http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/95.html
LANL: Americium - Basic information and history. - http://periodic.lanl.gov/elements/95.html
Lenntech: Americium - Physical data, chemical properties, health and environmental effects. - http://www.lenntech.com/Periodic-chart-elements/Am-en.htm
Visual Elements: Americium - Image, general and physical information, and key isotopes. - http://www.chemsoc.org/viselements/pages/americium.html