In the 2011 Affiliate Summit AffStat Report, where over fourteen-hundred affiliates were surveyed, we asked, “How do you most often find out about an affiliate program and then join?”, and 24% responded with “Search Engine.”
I frequently use search engines to find new affiliate programs to promote.
What I do is to search for the main keyword for my site, followed by the phrase affiliate program.
Sometimes the results are junky, but more often than not, I'll discover affiliate programs that didn't occur to me.