Welcome to this site! I'm a climate researcher and a meteorologist, so that might help to explain why my pictures are mainly focussed on clouds, landscape and weather.
After having spent a lot of time on flickr, I migrated to commercial sites in January, 2008. When you submit images to these sites, they are put in a queue for review and quite a few of them get rejected (usually for a good reason). This process has improved my photography by leaps and bounds. I now have a pretty good idea of what will pass, and it has taught me a lot about post-processing. Click on one of the links to the left if you would like to give it a shot.
I'm currently submitting to a few microstock sites: iStockphoto, Dreamstime, SnapVillage, PantherMedia and Fotolia, listed in order of subjective importance. In terms of money, it is definitely not worth the time and effort. As a consequence, I have deleted my entire gallery at Shutterstock, where they pay only $0.25 per download.
I'm also trying out the PhotoShelter Collection for fun. Their business model is different from the microstock one - more money for the photographer and much higher prices.
Because I know that many people are interested in seeing how others are doing, I post all my numbers, such as size of portfolio, balance, approval rate etc., in my microstock diary on my photography blog. Just click on the link in the menu to the left. The numbers might give you an indication of what to expect if you're just doing this for a hobby.
If you would like to buy a license for one of my images, browse my portfolio or just follow the links to one of my commercial galleries in the left menu. You'll also find my contact e-mail address at the bottom of the menu to the left. Enjoy!