What is a niche blog anyway?
A successful niche blog / or website / is a place where ( certain subject / object / or specific product or service )* is covered in it's full detail, explaining all areas and aspects, possible one stop place for all the people interested in this * leaving no place for the competition. If you are passionate bout something, or have a special knowledge on some subject - this is your niche. Just pour your knowledge into this blog and soon you'll be getting a strong amount of targeted visitors with interest similar to yours.
Once you achieve this - there's no limit on what you can do with this blog. Choose affiliate program featuring similar products or apply to the eBay Partner Network - it's up to you. The money will start flowing to you.
Visit my niche web store for an example.