Theres some good ones at http://www.affiliateseeking.com I prefer adsense. YPN is good if you are in the USA. TLA's is another.
John posted a good resource there. I think it depends too much on a few factors that vary to say something like "[PROGRAM] is the best by far". I'd try a few out on your sites to see which yields the highest return.
Adsung give 85% to publishers and pay via paypal on a monthly basis which is why you should check them out