Enter Quantcast. Quantcast.com is a firm/site that independently measures traffic and demographic data for popular websites. It was started by Stanford Statistics Professors, and now can be leveraged by us (recruiting professionals) to help evaluate whether a particular site attracts the kind of users we'd want to target in specialized online ads.
While it doesn't show job titles, it does allow you to slice and dice to see how many people fit your general profile.
So, if you're trying to build a case - based on data - on why you should run online ads on a big tech blog to go after those degreed, african american, under 30, New York based, $60k+ candidates with an interest in technology, quantcast can help. They can help you identify the right site, gather current data, and compare it to other options without having to engage an ad agency.