Tantalum-Niobium International Study Center
The Tantalum-Niobium International Study Center (T.I.C.) is an international, non-profit association. It has more than 50 members, which are companies involved in raw material production, processing, assaying, trading, capacitor manufacture, chemical process equipment manufacture, and are situated in more than 20 different countries across the world.
http://www.tanb.org/

LANL: Niobium
History, sources, properties, and uses.
http://periodic.lanl.gov/elements/41.html

It's Elemental: Niobium
The Element Niobium - Basic Physical and Historical Information
http://education.jlab.org/itselemental/ele041.html

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

H.C. Starck Inc.
Mo, Nb, Re, Ta, W Powders and their compounds, boron, borides, carbides, nitrides, AMPERIT®-Thermal Spray Powders, alloys, composites and parts. Functional Polymers: Anti-static and High Conductive Coating, OLED, Capacitor, Electroluminescence. Engineered ceramic parts made of Al2O3, BN, BC, SiC, Si3N4, ZrO2.
http://www.hcstarck.com/

Visual Elements: Niobium
Image, uses, general information, and ionisation energies.
http://www.chemsoc.org/viselements/pages/niobium.html

Lenntech: Niobium
chemical properties, health and environmental effects of niobium
http://www.lenntech.com/Periodic-chart-elements/Nb-en.htm

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

ChemGlobe: Niobium
The chemical element [Nb] - Niobium - Datasheet
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/41.html

EnvironmentalChemistry.com: Niobium
Comprehensive information for the element Niobium – Nb is provided by this page including scores of properties, element names in many languages, most known nuclides and technical terms are linked to their definitions.
http://environmentalchemistry.com/yogi/periodic/Nb.html