The Motley Fool has open site stock boards, but most don't get the quanity or quality of discussion as the boards exclusive to the paid services. I think there is an open YONG board, but it isn't as informative or active as the Global Gains board.
One of the few great open boards is the ATPG board. ATPG is not a recommendation on any of the services. It's better than the Yahoo ATPG board, although a few people cross post on both boards.
For value investors in general, the corner of berkshire and fairfax message board is a pretty good one. That one is moderated by Sanjeev Parsad and is based in Canada. Google it, it should have a .ca suffix. There are also many good private groups on yahoo that are by invitation only.
If you can write a good enough original investment write-up, VIC (Value Investors Club) - run by Joel Greenblatt - is one of the best forums out there. But you have to be admitted to get the current posts. Delayed posts are available to the public, I believe.
This board is pretty entertaining, but yahoo finance boards in general are so knee-jerk negative that it is hard to get any value out of them. Sometimes when a company is obscure enough, you only get the intelligent folks trying to make sense of a complicated situation, and then yahoo works best.
Thank you for the great responses. I'll probably have to pick up a subscription. However, I'm still curious if anyone posts at any boards other than here and the global gains board. This is a pretty decent board, but I find it hard to believe that a stock specific yahoo message board is the best public discussion forum out there!
I've been a suscriber for over 2 years. The 300 bucks a year is probably the best investment I've ever made. If you are interested in foreign stocks, especially Chinese, you get great coverage and the discussion boards are awesome compared to most Yahoo boards. They don't tolerate offensive posts and a lot of the suscribers are really sharp. (Like here on the Yahoo YONG board) The paid services are nothing like what you would expect from reading the daily noise generated by MF to generate traffic to their website.
It's also risk free. If you decide to cancel, you get all your money back if you cancel within 30 days. A prorated refund after that. I've tried and cancelled some other of their services and always got a ho hassle refund.