I don't read it as much as I used to, but if you're interested in barbeque and in particular, smoking using a Weber Smoker, I highly recommend this site:
The Virtual Weber Bullet
I like the Forum Romanum.
Smart group, they won't let me join.
ER is my favorite forum, followed by The Boglehead forums. Other forums I read, but not with regularity are electrical, air-conditioning and handyman repair.
Any others here read forums other than ER?
ER and Bogleheads are my favorites for financial planning. I also spend time on several golf, sailing, food(ie), travel/relocation, cord cutting, and automotive sites/forums. I am on forums to learn mostly. In that light- though not a forum, I use YouTube more than any single forum for non-fiction viewing. YouTube is so much more than cat videos and pop star wannabes as some may still think.