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C/D/N ISOTOPES
Quite a large listing of deuterated compounds and Carbon-13 and Nitrogen-15 labelled compounds. In English or German or French.
http://www.cdniso.com/
Cambridge Isotope Laboratories
Manufacturer of stable isotope labeled compounds and some fine deuterated solvents too.
http://www.isotope.com/
Isotec
Makes some of the most unique and novel labeled compounds
http://www.isotec.com/
Medical Isotopes, Inc.
Nearly a complete line of enriched biochemicals. Nice selection of fatty acids, enriched with C13.
http://www.medicalisotopes.com/