Paul,
Some time ago I used what was known as Key Systems (The Kornish Brothers) for 2 successful placements (for myself). First when I was coming out of the Navy in the late 80s and then later, after a couple of moves they found my second Chief Engineer's job for me. Overall the experience was positive and I would recommend someone like them.
On the flip side, I've attempted to use other placement services (the dot.coms) and have come up with nothing but a lot of spam, months after ending my search. In those cases, I was able to search and find plenty of leads, but nothing bore fruit.
I've developed the opinion that nothing takes the place of good old-fashioned networking. (I don't mean anything that involves CAT6e or WiFi). I'm talking about getting out there and involved in professional organizations, functions, whatever and getting to know other people who do what you do. That has been, by far, my most successful form of job hunting.