Nearly everyjob I have had has been through an agency and they have not charged me a penny. They get about 20% of 1st years salary from the employer though. This actually helped me get a payrise once, as I said was prepared to leave for more money and pointed out it would have cost my employer...
As an accountant I always have to go through agents to either get a new job myself or recruit for a position, and you have hit the nail the head. I can't deal with the slimey sales twats (the tan doesn't offend!). As said by someone else, the big high street agents are the worse for this