How long u have been using Ubuntu?? If you are using Ubuntu for a long time now and have had your hands-on many Ubuntu versions, then 'Ubuntu Artwork Archives' is an excellent place to take a journey down the lane and see Artworks for your favorite versions.
Even those who are using Ubuntu for first time or for not so long, it is an excellent place to see how beautifully Ubuntu Artwork have evolved over the years.
The archives include screenshots for themes, wallpapers, icons, GDM screens, cursors, usplash, bootstrap etc. All the Ubuntu versions right from Ubuntu 4.10 Warty Warthog to Ubuntu 10.04 Lucid Lynx are included. Ubuntu 10.10 Maverick Meerkat will follow once the final version is out on October, 10.
If you want to dig even more, you can go to 'The Ubuntu Museum' for screencasts and working virtual machine images for Ubuntu versions upto 9.04 'Jaunty Jackalope'.