American Association of Variable Star Observers
The largest organization for variable stars: provides professional and amateur collaboration, research, and analysis of variable star observations.
http://www.aavso.org/

General Catalog of Variable Stars Research Group
Research group working on the GCVS, Sternberg Astronomical Institute, Moscow, Russia. Includes catalogs and publications.
http://www.sai.msu.su/groups/cluster/gcvs/

Information Bulletin on Variable Stars
The IBVS is a bulletin of Commissions 27 and 42 of the International Astronomical Union, published by Konkoly Observatory, Budapest, Hungary.
http://www.konkoly.hu/IBVS/IBVS.html

Astronomy On-Line
Collaborative Project aimed at getting new people involved in variable star observing.
http://www.eso.org/outreach/spec-prog/aol/market/collaboration/varstar/

Free Virtual Galaxy Project
By Jim Smith's. Purpose is to provide a zero cost, interactive 3D virtual reality system.
http://www.ccm.net/~jrsmith/

Astronomical Society of South Australia
ASSA's variable star group. News, FAQ, charts, and software.
http://www.assa.org.au/sig/variables/

A Ritzian Interpretation of Variable Stars
A study on the nature of the speed of light in space using light curves and spectroscopic observations of variable stars as evidence.
http://www.ebicom.net/~rsf1/binaries.htm

Brigham Young University Variable Star Database
Currently contains 311 stars which have been classified as Delta Scutis or Gamma Doradus in some published source.
http://astro2.byu.edu/~vardat/

The Minima of Algol
An article by Alan MacRobert from Sky and Telescope Magazine about the star Algol (Beta Persei) was the first eclipsing variable star ever discovered.
http://skyandtelescope.com/observing/objects/variablestars/article_108_1.asp

The Top Twelve Naked-Eye Variable Stars
An article by John Isles from Sky and Telescope Magazine.
http://skyandtelescope.com/observing/objects/variablestars/article_160_1.asp

Skyandtelescope.com - Variable Stars
Observing variable stars.
http://SkyandTelescope.com/observing/objects/variablestars/

The Cepheid Distance Scale: A History
A critical review of the Cepheid distance scale, from its inception, to the Hipparcos mission and beyond.
http://institute-of-brilliant-failures.com/index.htm