Type in a domain name, keyword, or market niche in www.spyfu.com and you will get a list of criteria, such as Cost/Click, Clicks/Day and estimate number of advertisers.

The key value to look for is the Cost/Click. The more an advertiser pays for clicks, the more you were earn as a publisher or affiliate.

Use Spyfu to identify the most profitibale niches to pursue in monetizing your websites.