Santa Clara Valley Koi and Water Garden Club, meets every third Friday of the month
Cherry Hill Koi and Water Gardens, a local store
Koi Classification, a well-organized, nicely Photoshopped collection of "sample" koi to help with classification
Koi USA magazine, one of the few Koi magazines available
Feeding Koi, which pretty much sticks to that topic, but has a lot of useful information about it