I'd like to take this opportunity to present to you the Photographers guide to the different Microstock Agencies. The link should be at the top of the page: "Photographers Guide to Microstock Agencies". It's a short summary of the microstock agencies and details about each but it should be very handy. Keep in mind it is only based off of my own experiences and information I have gathered from other photographers. I hope it is beneficial to you!
Without further delay, I bid that you visit and read up on where to begin! Although it is primarily geared towards the beginner, any microstock photographer may benefit from some of the little insights gathered here.