Stock.xchng is an impressive collection of many high-quality photos taken by amateur photographers from around the world. Stock.xchng archives more than 100,000 images for which the photographers have established re-usage terms, leaving most of them available for immediate re-use. You can browse the library in multiple ways and the thumbnail views that are large enough to provide a good glimpse of what the picture contains. images are also available in different sizes so you can always obtain the best result for your design efforts.
Stockvault is a stock photo sharing website where photographers can share their high-resolution photos and images to use for personal and non-commercial purposes. Without even registering, you can browse Stockvault archive and download all the images you need. Photos are not offered in different sizes, but the standard resolution is generally high resoulting in large pictures. By registering, you also get the option to send a photo via e-mail or to use a lightbox, which is a feature that helps you bookmark images you like and create a set of photos for later use.
Pixmac is a “picture market” with a large section of free photos that you can download and use for your own website. Available sizes for free photos range from 0.1MP to 5MP. To download the image you can either register to the service or give your e-mail address when you hit the download button. For each photo you must check the license associated that rules use and re-printability.
Photoree is a free web service that helps you discover random images that are (mostly) under a Creative Commons license. You have to register to the site and Photoree will create a personal filter for you. Any time you browse and rate a photo, your personal filter will tune in with your likings by showing you only images that are relevant to your own tastes. For each photo you can check if the image is CC licensed and which specific type of license is associated.