Dreamstime
Buy and Sell Images at Dreamstime
D r e a m s t i m e

Sell Your Digital Images: Dreamstime pays $0.50 to $1.00 per basic download to the photographer (50%) and has a pretty good upload system. 

Buy Digital Images: Dreamstime charges more for photos that have been download 100 times or more, and again if they’ve been downloaded 500 times or more. They have also recently implemented a system where print and web images are separate purchases. You can currently download images for less than $1.

 

 
Extended licenses at Dreamstime
Dreamstime recently announced four new extended licenses which could increase earnings significantly: Increase Max Copies, Web Usage, Print Usage, and Sell the Rights. Each of these extends the ways in which the image can be used and pays a much higher premium. If you sell the rights to the image, you no longer control it and cannot sell it elsewhere, so use it with caution--noting that you can make a large chunk of change using this option (you can set your own price). Further details are below.