List of agencies to contribute:
Shutterstock - best selling agency for many photographers.
Dreamstime - a strong agency where you definitely should be present.
Fotolia - steadily developing and now on of the big players.
iStockphoto - big agency with good sales; weird upload process and high rejection rates.
BigStockPhoto - excellent representative of a strong mid-player with growing sales.
FeaturePics - smaller agency with nice commissions.
123RF - slower sales, but it's in the top-10.
CanStockPhoto - slower sales, but it's in the top-10.
Crestock - enormous approval delays sometimes and unpredictable rejection rate.
DepositPhotos - young yet ambitious, strict approval policy.
If you want to maximize your presence at microstock, consider registering with these agencies as well: