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.
The Brian Enos forum.
Down Range TV forum.
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.