To support the national system, join NARP http://www.narprail.org NARP was instrumental in creating Amtrak, and members get travel discounts that can pay for the membership.I believe it is NARP that holds an annual (springtime) regional members meeting in Oakland near the Jack London Square station.
Another good national organization is the National Corridors Initiative http://www.nationalcorridors.org
California has two regional organizations, which are somewhat in competition with each other, evidently due to some differences in philosophy. One is TRAC (Train Riders Association of California) http://www.calrailnews.com/ The other is RailPAC (Rail Passenger Association of California) http://www.railpac.org/ I am a member of the latter, but I get a little annoyed with it sometimes.
[This message has been edited by Mr. Toy (edited 07-27-2004).]