I would recommend Yahoo! Advertising in complement to the other two major SEM engines, Google and Bing. Paid SEM campaigns are the bread-and-butter of the digital marketing landscape. With Yahoo!'s display capabilities emerging, it's finally catching up to the other platforms in terms of sophistication. It integrates readily with marketing management platforms (like Kenshoo), and data export is a breeze. I would not recommend Yahoo! for the first deployment or market-testing phase of SEM, but getting up and running for a moderate budget will cover a clients' bases and ensure the best audience saturation.