I've thought about this space for quite a while, fragmenting job sites all charge money to the company just to post an ad. From that, you expect a user response. I think the ideal method would be to have an indexed, structured database of potential applicants, people who are interested in potential job offers. Company's then input their requirements and a list of potential applicants is spit out, no identifying information, just the raw skills/experience (10 years with C++, 15 with C, 2 with C#, etc.). The company then pays $x to solicit that potential applicant into applying for the job. This preserve's the anonyminity the current system has (no personal identifiable information revealed until application takes place) and allows companies to spend significantly less time attempting to discover potential applicants. It's not without it's massive drawbacks (you need the index of applicants, get companies to use it, get applicants to keep their information up to date, gives the applicant a feeling of not trying to find a job, HR does the hiring so they may not pay for the grey area applicants when normally they'd at least make it to the hiring manager) but you can overcome some of these by providing the traditional service as well, company's pay a "nominal" fee to list a position and applicants search/apply.
From what I've discovered, the best jobs are the ones you can't find. They're posted on the companies job listings and sit there, or the current job search systems have crappy indexes and include more cruft than quality (try a search for 'c linux' on one for a good example). Hmm...maybe there's room in this sector if one could tap into a large number of people who are interested in anonymously being considered for other potential job opportunities.