Well, I've worked in the webmaster/admin forum niche for a while, I've also tried my luck at creating an off-topic/general chat forum, and we actually got that forum to 30k posts before merging it a few months later, I even had a t-shirt made for it called "Offtopicbb". I also created a business forum with one of my buddies, but we ended up selling that to fund other projects. Now, I'm just working in the virtual pets/gaming niche. How about you? How many niches have you worked in?