Half-left has designed a new theme for Gnome Shell based on the Default Ambiance theme in Ubuntu. The theme looks great and if you use Gnome 3 PPA in Ubuntu 11.04, it would nicely integrate with your desktop.
- Backup /usr/share/gnome-shell/theme folder
- Download Ambiance Gnome Shell theme from here
- Extract the archive and rename gnome-shell to theme
- Copy this folder to /usr/share/gnome-shell/
- Restart GNOME Shell by hitting Alt+F2, then type r and press enter
You can also use gnome-tweak-tool for switching themes. For more Gnome Shell themes, you can browse Half-left's collection on DeviantART.
screenshot via half-left