When my brain's creative juices squeeze out, I do some stock photography. I'm able to do this very seldom and as a result a very low pool of stock photos in my Fotolia Portfolio. I've posted an ad of Fotolia above where I try to sell some of my stock photos.
The majority of my stock photos are food, toys, and some general objects. I'm planning to branch out in some stocks photos with some people in it.
If you're planning to do some stock photography, read through all the microstock agencies' terms and conditions. I've chosen Fotolia for it's ease of use.
If you're laying out some graphics, you can also consider Fotolia as a source of stock photos.