Equinox is a new GTK2 engine already used by themes such as Elementary.
There's a lot of catching up to do, and I'll start with the updated Light Themes package which landed in Ubuntu 10.10 Maverick Meerkat while I was away. To make it easy to install for everybody still using Ubuntu 10.04 Lucid Lynx, we've uploaded the Ubuntu Maverick version to the WebUpd8 Light Themes PPA.
I can't stand the default menu Ubuntu comes with and I only keep it because I have to know under which submenu the user can find an installed application when posting on WebUpd8. This wouldn't be needed if people used a menu with a search function but anyway. Also, since I install quite a few applications, half of it requires scrolling and makes it almost unusable.
Searching for something totally unrelated, I stumbled upon an amazing theme pack created by Izo called "SHI10 GTK Linux Suite".
New Wave is a truly awesome Gnome theme available in Ubuntu's community-themes package for quite a few releases.
Some community themes from the Ubuntu Artwork Wiki made it into the "community-themes" package from Ubuntu 10.04 Lucid Lynx (which you can install using: sudo apt-get install community-themes) however some amazing themes didn't.
The beautiful Bisigi themes were available for Ubuntu 10.04 Lucid Lynx users in a testing PPA. Well, today the themes have moved to the main PPA.
The latest ubuntu-mono brings package-supported icons with new logo for software-center, synaptic, new logos to distributor-log as well as a new logo for GDM: