ChemGlobe: Niobium
- Electronic, thermal, and steric data along with a table of isotopes.
- http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/41.html

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

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

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

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

USGS Minerals Information: Niobium
- Statistics and information on the worldwide supply, demand, and flow of the element (PDF format).
- http://minerals.usgs.gov/minerals/pubs/commodity/niobium/

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

It's Elemental: Niobium
- Basic physical and historical information.
- http://education.jlab.org/itselemental/ele041.html

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