PacketProtector is a Linux distribution for wireless routers, built on top of OpenWrt. The goal of this project is to transform the router into a unified threat management device.
All you need is a Linksys WRTSL54GS or ASUS WL-500g (Deluxe or Premium) router, and a USB 2.0 drive with 100MB of free space.
http://packetprotector.org/