Fluorine

It's Elemental: Fluorine - Basic physical and historical information.
http://education.jlab.org/itselemental/ele009.html

Visual Elements: Fluorine - General and physical information, source, uses, key isotopes, and ionisation energies.
http://www.chemsoc.org/viselements/pages/fluorine.html

ChemGlobe: Fluorine - Electronic, thermal, and steric data along with basic information.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/9.html

ChemicalElements.com: Fluorine - Basic information, atomic structure, and table of isotopes.
http://www.chemicalelements.com/elements/f.html

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

Britannica Nobel Prize: Fluorine - Detailed overview and data.
http://www.britannica.com/nobel/micro/213_9.html

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

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

LANL: Flourine - History, properties, uses, and handling.
http://periodic.lanl.gov/elements/9.html

WebElements: Fluorine - Extensive information on history, uses, occurrence, compounds, and properties of the element.
http://www.webelements.com/fluorine/