There are approximately 200 million products currently listed on Amazon in all types of categories.
However there are some restricted categories, which you can see here:
http://www.amazon.com/gp/help/customer/display.html/ref=hp_bc_nav?ie=UTF8&nodeId=200301070
Generally speaking we advise against trying to sell in those categories unless you have prior experience. Competition is usually fierce. There will be a better opportunity out there for you in a category that you do not have to apply for.