This is an alternative theme for gitweb (tested with git web interface version 1.7.4.2). It is strongly inspired by GitHub.
Fullsize screenshots available on kogakure.github.com/gitweb-theme.
The installation of this stylesheet is very easy.
Just copy the CSS-file gitweb.css into the gitweb folder. Best practise would be to rename the old file, in case you want to switch back.
If you see some missing things or errors, please post a comment.