This is not meant to be an exhaustive list. There are good forums and not so good forums, but these are the ones I’ve found that I like.
Glock Talk, where my handle FillYerHands got started.
A special shout to the Texas Gun Talk forum, whose admin Alan dropped me a note and spurred this page.
GeorgiaPacking, where a lot of us GeorguaCarry.org folk hang out.
The Brian Enos forum.
Down Range TV forum.
AR15.com, sometimes called Arfcom. A great all around gun neighborhood.
The Doodie Project forum. (Note that this forum gets hacked quite often by trolls, and might be down. Be patient.)
Rimfire Central, a great place to talk about .22s and the like.