BusinessWeek  has compiled a list of 150 Headhunters

In selecting the 150 recruiters for exclusive list of the World’s Most Influential Headhunters, BusinessWeek considered a number of factors, including: their individual reputations; their years of headhunting experience; the global scope of their recruiting practices; their accessibility and responsiveness; their high visibility within the client markets they serve; the recognition they enjoy within their firms and/or global executive search communities.

The information was provided in response to a BusinessWeek survey

See the full list: http://bwnt.businessweek.com/interactive_reports/recruiter/