Please post information on standards used for stable isotopic studies. Links below will take you to the IAEA and NIST sites where standards and their values are listed. Occasionally the values are further refined, so a search of the current literature can be useful. Please post relevant references here. Some labs develop their own working standards and make them available to the community at large, usually for a fee. Commercial concerns also supply standardized material. Also, other standard material, not developed specifically for stable isotope analysis, is used as a working standard among different labs. It is good to double check your own house standards at other labs. Formal interlab comparison studies and development of new isotopic standards are organized through the governing body (internationally, IAEA), and those announcements are usually posted on the Isogeochem list server.

Light Element Isotopic Reference Materials (C, H, N, O, S)
Click on the link below to see certified isotope values for light element standards.

Isotopic Reference Materials--Accepted Values with citations:
Commission on Isotopic Abundances and Atomic Weights - CIAAW
National Institute of Standards and Technology - NIST
International Atomic Energy Agency - IAEA
USGS Reston Stable Isotope Laboratory
IAEA TECDOC-825 (pdf, large)
Isotopic Reference Materials, sources:
IAEA Reference Products (reference materials, proficiency tests)
NIST (Light Stable Isotopes)
USGS Reston Stable Isotope Laboratory (Isotopic Reference Materials)
USGS Reference materials (not developed for stable isotopic studies)

Working standards, academic and commercial sources:

Please click on the PDF file below to access information on Air Liquide Stable Isotope Secondary Reference Gases:

Organic stable isotope reference materials (Indiana University)
Isometric Instruments Gas Standards
Standardized gas, small tanks (Oztech, e-mail)
Elemental Microanalysis (IRMS supplement, Isotope reference materials)
EA Consumables, Inc. (Isotope reference Materials)