They sent me an email requesting images. I have never looked into selling stock photos, thinking I don't have anything that might fit into a specific use etc. Have you sold images for stock use? Sounds like fun. Assuming that they actually sell.
I have one photo with the National Geographic Stock Collection that makes a bit of money each year, but they don't let you submit photos to them so just the one there. I signed up with iStock but haven't followed through with it and uploaded anything. I'd probably stick to the bigger U.S.-based companies if you're thinking of it. Shutterstock and iStock are both big and reputable. That one looks like they are discount which means less money for you. That and the overseas thing always sketches me out.
@wes242 might be able to enlighten us on stock selling.