Also, consider implementing a contest to your forum here and there. For instance: the first member to reach 1,000 posts will win themselves a game, or something. And runners up will receive a small cash reward, perhaps. I can't think of decent prizes just off the top of my head at the moment but I'll be offering a chance to win a free copy of Fable 2 for Xbox 360 on my
Fable 2 website and I'm confident that it will help attract some attention.