AAVSO - The American Association of Variable Star Observers - the largest variable star organization in the United States if not the world. A great web site.
Eclipsing Binary Observers Home Page - A subset of AAVSO eclipsing binary observers and others active in scientific observing of EB's.
VSNET - A web site and network of mailing lists run from Japan. A very active entity where the latest happenings in the variable star world are discussed. Just be careful not to sign up to be automatically added to new mailing lists. Your drive may fill up before you can get yourself unsubscribed!
There are many many more interesting places to go to learn about variables, how to observe them and the observers themselves and their techniques. I'll add them gradually here. In the meantime, the links pages at the above sites will occupy you for hours.