FreePixels offers free high resolution stock photos for use in both personal and commercial design projects.

There is a large collection of stock images here and are of high quality.

Legal (taken from their Terms of use)

This is a license, not a cession. Freepixels continue to own the intellectual property rights of the images and digital creations. The images and digital creations are provided under the terms of the following license agreement that states what you may and may not do with them.

Freepixels grants to you a non-exclusive, non-transferable license to use and reproduce the images on the terms and conditions contained in this agreement.

Every Freepixels image or digital creation used must retain the domain name: freepixels.com when used on the internet, in a web page, in printed publications, or in any product, advertising, or packaging. This credit, however, may be cropped out or digitally removed from the photograph if it is included in readable type near each photograph, group of photographs, in the text, or in the credits.