If you are in the business of trying to market your website or products online then we highly recommend using
Yahoo's Search Marketing platform.
Why? Because the traffic is of extremely high quality. We have done our own marketing (for this site and others) and have used all of the major methods of traffic acquisition and we've found no traffic that converts better than Yahoo's paid traffic.
Not only that but they now offer a free $25 credit for signing up with a new account.
Along with being able to purchase paid ads in Yahoo's search results you can also purchase paid ads on major websites like CNN.com through Yahoo.
Everybody thinks Google first when they are thinking about buying ads online (and for good reason) but we've found Yahoo's traffic converts even better even if there isn't quite the volume of Google's AdWords.
Yahoo's Search Marketing - $25 Free Credit - Click Here