You can do this by building a social network with tools like newsletters, Craigslist, and candidate referrals and constantly working on your SEO. I’ve blogged about that before as well as
The real trick though consists of constantly putting yourself in the shoes of the candidate. Recruiting younger candidates? Buy yourself an Ipod; cut your next job ad as a podcast. Recruiting chemical engineers? Attend local BOF meetings.
Finally, ride the wave of free search technologies. My latest favorite: GoogleBase. With it, you can place free ads and leverage Google maps to visisualize job and candidate locations.