Xiombarg asked about the Adventure Trade Organization, which I still haven't heard anything about.
I do want to put in a plug for the Game Publishers Association, http://www.thegpa.org/. I've found my membership there to be $60 well spent (although I'm not sure the $20 associate wouldn't have suited me just as well). The great advantage of their listserv is that it features discussion from a wide range of professionals throughout the "mainstream" industry, who are remarkably willing to provide snappy answers to stupid questions.
I just sent a similar plug for the Forge through the GPA listserv. I hope the cross-pollination of different sets of experience & ideologies will be fruitful for both communities, and that y'all will excuse me if this was a breach of netiquette.
Hi,
I'm Patrick Sweeney of Firefly Games, and I'm the executive director of the Game Publishers Association this year.
I'm happy to answer any questions you may have about benefits of joining or how to join. Please feel free to contact me at patrick@firefly-games.com or visit the GPA site at www.thegpa.org to find out more.
I'll try to check back on the forums for questions, too, but email is a better way to contact me as I don't regularly visit the Forge anymore.
Thanks!