I have been trying to think of cool ways that I can make my forum exciting. It is a general discussion forum, so there is a lot of competition in the niche. What is one thing that you have always wanted to see on a general discussion forum?
Failing that, topics that get people talking are things like soaps, current affairs (although that can make work for Mods!) and we've found that people like the 'lists' things - for example top five of a certain category (favourite films perhaps), or hypothetical ones such as 'who would the six guests at your dream dinner party be'.
It's hard to really get a general discussion forum going, and known, just due to the intense competition. I'd say look at what the big ones are doing and one up them.
I would add things like chat boxes (as general forums tend to be chat rooms) and possibly special sections that are automatically gained through post count. Like they join another group when they hit x number of posts and then they can view either more mature or special forums.
Chat boxes decrease activity by a lot on the forums. The special access idea sounds good. Also try to implement a shop for custom user titles, banner spots, username change, etc..