My favorite's Neverblue at
NeverblueAds™ Affiliate Network | Home
They have great offers, excellent payouts, top notch support, and a fantastic selection of ad copy (banners, etc) and they also have a super easy to use banner rotation system. The admin system is a breeze to use and very easy to find offers, select copy, do reporting, etc. I give 'em an 11 out of 10!
I'd like to work more with azoogle, but they need to offer more of the features that NeverBlue offers. Plus I find their new admin area very, VERY confusing to navigate. Maybe it's just me, but it's not very intuitive for me at all.