RSS: http://api.flickr.com/services/feeds/groups_pool.gne?id=17274427@N00
(Cream of the Crop Flickr feed)

Flickr.com is an online photo management and sharing website which means it's a great place to find the wallpaper that fits you exactly. Searching for Flickr feeds of users or groups that have similar interests will provide you with an unlimited variety of pictures to see every day that match your particular tastes.

Image sizes vary from image to image though and not all users or groups post new images daily. So if you know of a great Flickr feed, feel free to add it to this post.