Major Pay Per Click Search Engines

Yahoo! Search Marketing
Put your business in front of potential customers at the precise moment they're searching for what you sell.
LookSmart
LookSmart is primarily a human-compiled directory of websites. It gathers its listings in two ways. Commercial sites pay to be listed in its commercial categories, making the service very much like an electronic "Yellow Pages." However, volunteer editors at the LookSmart-owned Zeal directory also catalog sites into non-commercial categories for free. Though Zeal is a separate website, its listings are integrated into LookSmart's results.
Google Ads | Generate Leads with Online Ads
The Google AdWords program places paid listings within google's search results, as well as on some other sites that carry its listings.