Possible Duplicate:
How do I change to a theme not listed in the Appearance screen?
why does ubuntu unity only have 4 themes to chooes? ambiance, radiance and 2 high contrast-themes
it would be so great if there would be more themes to choose
thanx
SnapOverflow
Check this out.
http://www.upubuntu.com/2012/02/12-new-best-gnome-shell-themes-for.html
These work in Unity perfectly Source upubuntu.com
It's plenty of themes, just have a look at this great site: Ubuntu Unity Themes
In fact, they are just 4 installed by default because they have fo fit into the 700MB live image ;)