I have been frequenting online message boards for years.
These are the ones I haunt the most in order of frequency:
Troll Lord Games
Since the onset of 4e and the resulting dry up of 3.5 support, I grew more interested in Castles & Crusades and, as such, found a new home at the TLG forums. A real nice group of people posts here regularly. It's a small community, but a loyal one. C&C is obviously the focus, but they talk about gaming in general.
Most of my 3rd edition D&D experience has revolved around Necromancer Games products, particularly Rappan Athuk which was been my main source of campaign material for years. The forums aren't very active these days and most of the original crowd has moved on. However, with the recent release of a few back-logged 3.5 products, there has been more activity there as of late. It's nice to see Bill Webb posting again. He is the main author on most of my favorite NG products.
ENWorld is a great place to get general RPG news. The forums are extensive and, by and large, civil. I don't post there too much as the majority of the subjects never grab me. Perhaps it's because I'm more interested in discussing particular gaming products rather than gaming in general.