BigStockPhoto

You won't need images often, but once you need them, it's better to get them cheap and legally. I spent some time, and here is the service I ended up with: BigStockPhoto.

Huge selection of stock photos and some illustrations, you pay only for what you use, no expensive subscriptions, and a single photo normally costs a buck or a two.

What else could I say? I am really impressed with them. Will be you? If you in a need for images, go and check.

Of course, keep in mind that unless design is your bread and butter, in most cases, you won't need stock images at all. It will be provided to you as part of the outsourced design services.