Choosing a niche to market in comes down to more than just what you know. Many articles on internet marketing will tell you that you should stick to a topic that you are knowledgeable and passionate about, but when you are running several hundred sites this just isn’t practical, or necessary (if you are running many sites then you need to be hiring content writers who will research the topics and write for you).
My friend John posted a useful list of niches at his adsense blog. Looks like his experiences are pretty similar to mine, although I have never worked in the automotive arena. Maybe I should, I can just imagine myself swanning around in some of the cool cars you can rent in Vegas… the job might have perks 
