This website: http://ubuntu.ecchi.ca/wallpapers/ is an archive of all wallpapers used by the Ubuntu distribution from Ubuntu 4.10 “Warty Warthog” to Ubuntu 10.10 “Maverick Meerkat”. Very cool if you want to see the classic old Ubuntu wallpapers that older releases used. Even the Ubuntu calendar wallpapers are present. These were removed from the Ubuntu repositories after the 8.04 release. So have a look and see if you see anything you like.