I run hackerjobs.co.uk and for the last year or so we've been providing free job listings. Despite that, we only get employers sign up as and when they need to

I run hackerjobs.co.uk and for the last year or so we've been providing free job listings. Despite that, we only get employers sign up as and when they need to post a job. We get relatively decent traffic considering we haven't paid a penny for marketing or advertising and ultimately, our most successful technique to get new employers to sign up is to personally email them directly when I see them advertising elsewhere. One of our biggest traffic sources come from aggregated job boards such as indeed.com and we find twitter to be surprisingly effective when we post new blogs or tweet about new jobs. All that said and done, onion2k's 5 points are very valid too.