Southern California Clubs
Los Angeles Wheelmen - the largest bike club in the LA area
Foothill Cycle Club - Pasadena and surrounds
SCOR Cardiac Cyclists Club (sponsors some interesting rides)
Covina Cycle Club -New
State & National Biking Organizations
Hosteling International/American Youth Hostels
The League of American Bicyclists (aka - The League of American Wheelmen); the national organization for American cyclists
Los Angeles Council of the HI/AYH (our local council)
San Diego Council of the HI/AYH
CABO - the California Association of Bicycling Organizations (not actually a home page, but has lots of information about cycling politics)
Other Sources
The Bicycling Event Guide - provides information on lots of rides, tours, centuries, fund raisers, etc.
The Internet Bicycling Hub (more than you ever wanted ...)