With the excitement over the anticipated new Ubuntu 10.04 release on April 22nd, and its new themes, there are 2 new themes. They are a dark theme called Ambiance, and a light golden theme called Radiance. You can make your existing Gnome desktop have these looks and they will be shown below.
Below is the darker theme similar to Ambiance. It is a combination of the Equinox Radiance Theme and Ambiance Metacity window treatment. You can find the Equinox Radiance Theme here at gnome-look.org http://gnome-look.org/content/show.php/Equinox+Radiance?content=121883
Below is a theme similar to the Radiance theme in 10.04. The Lucid Light Glossy theme along with the Radiance metacity window treatments is shown. It is very mac-like but with a touch of gold/tan in line with Ubuntu's color schemes.Available here from Gnome-look.org at: http://gnome-look.org/content/show.php/Lucid+Light+Glossy?content=121397
Below is the Karmic Theme. You can find it here to download: http://www.ubuntuthemes.org/karmic.html . It is a little lighter than the Shiki Dust Theme seen earlier. I've also included some wallpaper showing the new Ubuntu logo.