Scores of search firms (aka headhunters) serve law departments. Despite my teasing post of Oct. 26, 2005 on sources of law department lawyers and a more recent factoid on June 27, 2006 about 5 percent of hires coming through recruiters, I suspect that at the high end of law department hires search firms carry most of the water.
These firms have databases of potential recruits and they preserve the confidentiality of the hiring law department, they sift through piles of resumes and call contacts to interview them, they have a sense of market compensation and are able to compare positions, they are trained to assess people and they can help wavering candidates. Sometimes search firms even provide ancillary services along the lines of consulting.
The other side of the ledger points out that they typically charge a third or so of the first-year salary of recruits they find. Second, they might recruit from your law department, based on what they have learned. Third, you have to choose and work with one, which is akin to choosing a law firm on a matter. And, search firms may try to cross-market work with other departments.
Among the best know for senior level law-department positions in the US, among the large recruitment firms, are June Eichbaum of Heidrick & Struggles; Catherine Nathan of Spencer Stuart; and Julie Anne Goldberg of Korn/Ferry International.