Over 3 million images starting from 1$ for Medium size images. Free sign-up.Categorized. Great search engine.

Can't get bigger than Getty Images in this business. I don't think you can imagine picture and don't find it here.

Big name in the business of stock photography. Big site to say at least, you can find anything here.

Cheap means 1$ for small size images (web only). Print-quality images cost 3$ and very high resolution images cost 5$. Nicely categorized, no registration.

Subscription based stock agency - download 3600 images/year for 79$. Great selection fo photos. Easy navigation.

More than 800.000 images starting from 1$ for low resolution images and 2$ for print quality images. Free registration is required. Powerful search engine.