What is the most profitable affiliate program?

My suggestion would be the Amazon program. Typical 4-5% with an increase after you send over 1k in sales through Amazon. The big difference is that individuals who land on Amazon from your link can purchase anything and you get that percentage. Ex. you send them there for a music download and they buy a TV, you get 4% of that TV sale, plus whatever other things they bought.

In my opinion, Amazon is the most profitable affiliate market.