The Firing Line is decent, but does suffer a bit from the know-it-all syndrome, and like most gun boards is overrun with nitwits that think "tactical" is something you buy, and that a rifle is only useful if it had 12lbs of crap hung off it. I am not as familiar with the pistol forums there, but the rifle, C&R and handloading boards are pretty good. There are a few folks there who do know a lot, and are not dicks about it.
For old stuff, I like
Surplusrifleforum and
Gunboard's Forums
For Californians,
Calguns.net is top notch.
Tom