Yahoo and Google are a little pricey for me as they use the bidding system for keywords. Most of the keywords that apply to my site are going for around a 80 cents to a $1 a pop, give or take. Since my sites are basicly free I would loose to much money. Only about 5% of my traffic converts to affilate sales. So I need to keep under 10 cents a click to see any return on investment.