The National Archives Experience website has super high resolution images of the Declaration of Independance, The Constitution of the United States, The Bill of Rights and all of the Amendments. They are interesting texturally as well as historically.

I was looking for an image on google image search this morning and found that they had added huge image searchThanks google!

wallpapers (1024×768 minimum) is the mother load of high res flickr groups. It is chock full of images tagged with wallpaper at a minimum resolution of 1024×768. 36,669 images and counting. This will take a while to go through.