I have looked around a bit and found a few sites that have some links, but nothing comprehensive, so if any one knows of such a directory, I'd like to know it.
As for other forums, the only other one with which I'm currently registered is ar15.com. For reasons not fully understood, I've developed a late-in-life lust for a black rifle.
While there are some good forums out there, most of them are pretty poor compaired to this one. At the risk of sounding like kiss up, this may be the best firearms forum around today, for a couple of reasons.
It is well designed, well administered, and moderated with an even hand. The rules are reasonable and they are enforced.
The people who post here either know what they are talking about or are trying to learn (and most here fall into both catagories). While every once in a while someone will hit a nerve, the people I have followed on this forum usually treat each other with respect and good manners. That is not the norm on the i-net.
That's my take, anyway.