While the success rate at finding jobs through job boards, etc. is low, it is definitely worth pursuing. I use four channels:
For listings that appear on the aggregator sites, I would not click "Apply" on the listing (I don't trust the application that comes through those sites) - I would go to the hiring company and apply there (most often it will be the company domain name with /careers, but if not, you can navigate to the right page). If the listing was posted by an agency, look for a hint of the company name in the job description (it is amazing how often they creep through), and if you can figure it out, go directly to the company.
My other recommendation is to look in Linked In for anyone you know who is at the company, and follow up with them to get them to say something about you - many companies use automated filtering software, and you want to make sure that you are noticed in case you didn't use exactly the right keywords to make it through the filter. Besides, often the person will get a referral bonus if you are hired!
Recognize that for most of these guys, it is a numbers game, and you are just someone that they might be able to put into a position that will earn a commission. (For those at Percussion and Axceler, the sales style was borrowed directly from that developed at Stride.) So, you need to do the same - they are just a number to you, and they may or may not pan out, but it's worth a small investment.