I am constantly customizing my desktop with different themes, colors and wallpapers. I'm going to list here my five most favourite Gtk themes.

Shiki-Colours

Shiki-Colours: The orange themeThis is meant to be a hybrid theme between a dark theme and a light theme. So it isn't too dark, or too light. I find dark themes to be a bit depressing, so this is a very welcome theme to my collection.

It is available in various different colours: orange, blue, green and red. You will need Murrine SVN for it to work, but a Clearlooks based theme is also available. This will work with any distro using GNOME. If you're using Ubuntu Jaunty Jackalope (9.04) you're fine. More information is available on it's page on Gnome look.

Personally, I think that orange theme would be great on Ubuntu