here is my submission.
My favorite PPC engine has got to be the little used 7Search.com network of sites. They are my favorite because my deposit lasts a few months and I am usually paying $.10 for top keywords and am in the #1 spot. The traffic isn’t as high quality as AdWords or YPN, but the fact that I get traffic for about 1/4 of the price of tier 1 engines means that only half the traffic needs to be real people. It has worked out great for arbitrage!