AAVSO
http://www.aavso.org/
The American Association of Variable Star Observers (AAVSO) is a worldwide, nonprofit, scientific and educational organization of amateur and professional astronomers who are interested in variable stars. Its purpose is to coordinate, collect, evaluate, analyze, publish, and archive variable star observations made largely by amateur astronomers, and to make these observations available to professional astronomers, researchers, and educators. The AAVSO has an active Photoelectric Photometry Committee and observing program.

WGPAC
http://www.aas.org/wgpac/index.html
The Working Group for Professional Amateur Collaboration (WGPAC) provides a forum for collaboration between amateur and professional observational astronomers. The working group was created by the American Astronomical Society.

CBA
http://cba.phys.columbia.edu/
The Center for Backyard Astrophysics (CBA) is a global network of small telescopes dedicated to photometry of catalysmic variables.

SAS (Formerly IAPPP - West)
http://socastrosci.org/Default.htm
The Society for Astronomical Sciences (SAS) can trace its roots to the International Amateur-Professional Photoelectric Photometry (IAPPP). The role of the IAPPP was to facilitate collaborative astronomical research between amateur, student, and professional astronomers, by providing a medium for the exchange of practical information not normally discussed at symposia or published in other journals. SAS helps to continues that role.