I am in the process of starting a business directory. Right now, I am doing a general business directory, but eventually I will be doing niche "category specific" directories. The problem I am having right now is trying to come up with general categories. I would like to include all businesses, but I don't want to have hundreds of categories and subcategories. I have looked at the major directories, such as yelp, citysearch, yp, business dot com, etc., and all of them have different ways of doing it. I thought about just doing listings by business name...a through z (a, b, c, d, and so on) and setup tag keywords for each business type.
So for those that are running business directories, what categories are you including on your business directories and are you receiving a lot of requests to add more categories and subcategories? Any example business directory sites?