All but one job I've ever held has had at least some form of reference to get me in the door.
Many have been from direct personal recruitment on the part of a former colleague who wanted to work with me again.
Recruiter and completely took me by surprise. I was looking as I was in a horrid 'survival' job but hadn't turned to this one resource. It was an excellent call out of the blue.
Recruiters and a plethora of job posting sites like Monster, Dice, and jobs. Weeding through the junk is the tough part.
Recruiter. Was just casually exploring the market to decide whether to begin a job search in earnest, and they happened to send me something that was a good match for the next stage of my career development.