The following sites are sources for interesting examples of computer graphics.
www.cgsociety.org is the site of The Computer Graphics Society (CGSociety). Without being a member, you can browse the galleries and portfolios and get a good overview of the current work of computer artists.
art.gnome.org has a different purpose. It is a gallery of icons, backgrounds, and other artwork for changing, and hopefully improving, the visual appearance of your GNOME desktop.