The list of pro photo associations and organizations goes on an on. There's international and national groups, as well as groups for states and specific cities. There is also groups for specific types of photography and camera equipment.
Most of the groups require a membership, but offer quite a bit in return. Some of the large ones host annual conventions and trade shows, competitions and awards, and even have certified pro photographer programs. Pretty much all of the groups offer meetings, newsletters, and great networking opportunities.
Here's some you may want to check out (listed US or Non US. International groups are listed by where the headquarters are located)...
* AIAP- Association of Independent Architectural Photographers
* AIPAD- Association of International Photography Art Dealers
* APA- Advertising Photographers of America
* ASMP- American Society of Media Photographers
* ASPP- American Society of Picture Professionals
* NANPA- North American Nature Photography Association
* NPPA- National Press Photographers Association
* PACA- Picture Agency Council of America
* PFPO- Professional Fashion Photography Organization
* PMAI- Photo Marketing Association International
* PPA- Professional Photographers of America
* SAA- Stock Artists Alliance
* WHNPA- White House News Photographers Association
* WPJA- Wedding Photojournalist Association
* WPPI- Wedding and Portrait Photographers International
* WIPI- Women in Photography International
* ACMP- Advertising, Commercial, and Magazine Photographers of Australia
* AIPA- Advertising and Industrial Photographers Association, New Zealand
* BAPLA- British Association of Picture Libraries and Agencies
* BPPA- British Press Photographers Association
* CAPIC- Canadian Association of Photographers and Illustrators in Communications
* CEPIC- Coordination of Picture Agencies and Libraries
* PIAG- Presse Informations Agentur Gmbh
* PPofI- Professional Photographers of Israel
* PRA- Picture Research Association
* TV- Associazione Nazionale Fotografi Professionisti
Again, there's WAY too many to list here, but if you're looking for a specific format, equipment, or local group, your best bet is to do a web search. There's also a few other websites that list some different groups here, here, and here. And if I've left out one of your favorites, feel free to share it in the comments!