Image*After offers a good selection of high-resolution images for download.
There is a good selection of textures, nature architecture etc. Search results can be sorted by colour.
The larger images (top and bottom) are stock images; there is a charge for using these. Beware of using logos!
Images can be used in your own work, either personal or commercial, modifed, redistributed or sold as part of printed work. (terms at the time of writing)