These two sites so far have been very easy and upfront about your earnings and payments.
Helium so far seems to be the more profitable. However, you have to do a lot of self-promotion. Sometimes I feel as if I am promoting myself more than writing. That said, it is enjoyable.
Wikinut has been great so far. I have been able to duplicate any article I have written I own the rights to. One step at a time it is working. Let's just hope these two sites pan out for me as much as I am for them.