ChemGlobe: Rubidium
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/37.html

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

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

It's Elemental: Rubidium
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele037.html

LANL: Rubidium
   Sources, properties, isotopes, and uses.
   http://periodic.lanl.gov/elements/37.html

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

Radiochemistry of Rubidium
   Full text of the monograph by G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
   http://lib-www.lanl.gov/cgi-bin/getfile?rc000003.pdf

Visual Elements: Rubidium
   Image, source, uses, physical information, and key isotopes.
   http://www.chemsoc.org/viselements/pages/rubidium.html

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