CLickbank is very easy to sign-up and follow, also there are a lot of high quality products there to promote.

But it doesnt work in all countries. ANd it is easy to lose your affiliate checks to others.

CJ. com works in all countries and has phisycal products too, but very frustrating to sign -up and to track your results

Paydot.com is relatively new project, but I dont like it.

Orxan