Check out
www.retroread.com with your Kindle browser. You can browse or search titles and download them directly from your Kindle's browser. It is a "dumbed down" Kindle aware experience.
Accessing
www.retroread.com from a normal browser gives you the full site, where you can register and upload your own Google epubs for conversion.
(
www.retroread.com is all about converting Google epubs to mobi. There are currently 1500 titles in the library and dozens added daily.)