Classic Rendezvous. They have a Very Serious email-based discussion group, and extensive and very worthwhile archives of the aforementioned email group. Luminaries like Sheldon Brown, Brian Bayliss, and Hilary Stone are regular discussion members. If you join, remember that nothing post 1982 gets discussed, and topics other than old bicycles/memorabilia are verboten. If you post something for sale without a price fire will undoubtedly rain on your head. There are other rules, but you get the drift...