My experience is that LinkedIn is the way to go. If you have a thorough, well-written profile, the agents and internal HR professionals will come to you, because they're searching for keywords and locations. It's basically an online tool for SEO-ing your CV.
At the company I recently worked for, there were two people on the HR team whose entire remit was to recruit via LinkedIn. They didn't have any hand in day-to-day HR tasks, just spent their days on LinkedIn, communicating and arranging interviews with potential candidates.