Shutterstock still leads all the stock sites in how many sales we get each month - which translates into the highest earnings.
Istockphoto is really taking a turn for the terrible - as I can't remember the last time we made that little since we started.
Dreamstime is slowly creeping up on Istock and could end up being our #2 lifetime earner soon enough. It's still not too high, but it consistently makes between $20 and $40 a month. And because of the image contest they do every month, I always want to create something for it, so we've ended up with a lot of exclusive files that sell at a higher price point on this site.