Microsoft and Yahoo would make sense. Although the addition of AOL for Microsoft would also be appealing as the 2 main players for SE traffic is Google then Yahoo.

Speaking of Yahoo, I noticed that a few people mentioned they had success with Google but not Yahoo. I find my situation to be quite the opposite with my one site especially: www.cleancreditonline.com. I would be more than willing to collaberate with one or more individuals about "swapping" SEO methods used to obtain SE positioning and traffic. If interested please send an email to me at tlj_maxx(at)yahoo.com