Hey All,
I've documented the steps to build a TP-Link TL-WR703N travel router as a pen testing drop box similar to a Pwnie Express (using OpenWrt). 

http://www.minipwner.com/index.php/minipwner-build

The WR-703N is not as powerful as the Shiva Plug used for the Pwnie Express, but the travel router is smaller, can run off a battery, and has integrated WiFi.

Kevin
GIAC GSE, PMP, GCIH, GCIA, GCFW, GCFA, GSEC