As a profitable and low cost alternative to the 'big boys' take a look at advtiser[dot]com It pays 70% commission on all cost per clicks for publishers. For advertisers, there is a geo-specific targeting system which goes right down to city & town level. You choose where anyone can view your adverts from anywhere in the world, right down to just your local town or city. So if you have a business serving only a local area, only people browsing the web from withing that defined area will see your ad. This means that, for the first time, PPC advertising becomes a viable and powerful tool for small & medium sized businesses. For example, if you are a plumber in Austin, Texas, you will just get ad clicks from Austin, Texas (because it would be silly to travel to NYC or wherever to unblock a toilet!!). As soon as I reach the required posting threshold (please notice, mods, that I am not doing B.S. bumps or anything to get my count up) I will edit this with a link.
Google leads the way with its increasing share of paid search, primarily from its pay per click service, AdWords. Traditional media is losing its market share as ad dollars move to online marketing, and specifically the paid search arena. Advertisers enjoy PPC advertising because it is simple, they have greater control over their ad campaign, and they receive better feedback on its performance. The growing importance of online marketing makes PPC an important arena for them to use and master and in fact, it's not uncommon for CEO's to do their own company's PPC campaigns.