You can also go through SEO companies. Usually they get special rates for advertising so much on google, yahoo and so on. If you are willing to spend like, $2000 a week in adwords they can triple the traffic to your site for the same amount. Where you would end up spending $1 per click they will spend maybe half that for better results. I know of one SEO company in particular that is good but not sure if I am allowed to post it here or not.