Business / Search Engine Optimization (SEO) / AdWords: Google's advertisement and link auction network. Most of Google's ads are keyword targeted and sold on a cost per click basis in an auction which factors in ad click through rate as well as max bid. Google is looking into expanding their ad network to include video ads, demographic targeting, affiliate ads, radio ads, and traditional print ads. AdWords is an increasingly complex marketplace. One could write a 300 page book just covering AdWords. Rather than doing that here I thought it would be useful to link to many relevant resources.
Business / Human Resources (HR) / Demographics: The physical characteristics of a population, such as age, sex, marital status, family size, education, geographic location and occupation. MORE
Business / Search Engine Optimization (SEO) / AdCenter: Microsoft's cost per click ad network similar to Google's AdWords. While it has a few advanced features (including dayparting and demographic based bidding) it is still very easy in nature compared to MORE