My Genesis starter child theme. I tweak it pretty much every time I build a site with Genesis and find a new way to improve it.
I prefix everything with xchildthemex because I run my genesis-jumpstart.sh setup script at https://github.com/davidrgreen/wpdev-jumpstart-script in order to complete the setup. It installs the plugins I commonly use, adjusts WP options, cleans up the install, etc.