Kenzer and Company Forums - Home of the Kenzer and Company games such as HackMaster and their wonderful magazine Knights of the Dinner Table. I used to admin for these guys but now I mostly just lurk on their forums.
Serebii Forums - Home of major Pokemon discussions! You didn't think I would leave off a forum that deals with Pokemon, did you?
Dharma Secrets Forum - A home for all sorts of discussions on the TV show Lost. This forum is chock-full of Lost goodness. However, you need to register because during peak traffic periods only registered users can use the board.
That's it. Feel free to check these boards out.