I think the best places are Google Adwords, Yahoo or other similar SEs. You pay BID for keyword placement so if you know that there is no one using some keyword than probably you will have to pay almost nothing for click and you will be on the first position.
If you think about it and you know how many clicks are needed to make a sale in awarage "conversion rate" than you can calculate how much you can spend for a click to be in a profit. So you can sell some products via affiliate programs and make money... All you need is to find the right product and right keywords :idea: