If you want something interesting to think about, check out GumGum.
Instead of the usual stock model (you buy image from us to use in specific ways), GumGum is trying to hit the low-end market for online images.
For instance, suppose I have a blog entry about... say... microstock, and I want to liven it up a bit with an image. So, I go to GumGum, select the image I like, and post a link to it. GumGum serves the image, tracks views, and either charges me or puts advertising on the image. It could be really revolutionary for the small circulation web-site uses!
Or, I suppose, it could flop... I guess we'll see, won't we?