GluebyRue is a GTK3 theme for Ubuntu 11.10 Oneiric Ocelot that is compatible with Gnome Shell and Unity. The theme is a mixture of Adwaita and Evolve themes. Here is a screenshot of it under Ubuntu Oneiric:
You can beautify more this theme by selecting an icon theme from this list.
Via the terminal run these commands:
wget -O GluebyRue.tar.gz http://goo.gl/gy9nB
tar -xzvf GluebyRue.tar.gz -C ~/.themes
Enable now GluebyRue with tese commands:
gsettings set org.gnome.desktop.interface gtk-theme 'GluebyRue'
gconftool-2 --set --type string /apps/metacity/general/theme 'GluebyRue'