Mobile version of every website, is becoming a very important part of equation too. In order to make the most of it, I recommend signing up to:
Bitter Strawberry, and
Sex Goes Mobile
These are the most profitable, and the most important ones. You can also try:
First Mobile Cash, and
VPS Mobile
They may turn out to be better / more profitable, than the first two. Not everything is for everybody, and it largely depends on the site.