[sdragon]

#1: Google Adwords -see things from the other side of the equalation.

So, basically you go, sign up (best spent 15 bucks, ever), start a new compaign, and type in a web site with similar content to the one you're about to build; select all collected keywords, which are related to your venture, and behold the traffic estimator. Two points of data are of interest for you here: estimated avg CPC, and estimated clicks/ day; the first one will tell you how much you would earn _relatively_ to other keywords (remember, G takes a cut); the other will tell you how much of a niche you are.

#2: fail fast: you actually go out, and build a stub of your grand vision, stick up the ad network of your choice (it's always best to shop around), and measure it. You'll get much better data, than any other method -both from ad networks, and as market research (whether people would actually use your stuff) Good luck.