1. Shutterstock
2. Dreamstime
3. IStock
4. Fotolia
5. 123RF
6. Bigstock
7. Canstock
8. Alamy
9. MostPhotos
10. YayMicro
11. Veer Marketplace
12. GraphicLeftovers
13. The3DStudio
14. DepositPhotos
15. CutCaster

I’ve had wildly different success on some sites than other people.  Test them, see what works for you.

Of the sites most people are not on, GraphicLeftovers produces the most regularly for me.  GL beat all of the bit players for me and is close to catching Bigstock, 123RF and the rest for “top 7″ status.