1. Adding a GPS
Adding a GPS to your router may seem like an odd idea, but it does have it's uses. If you like to war drive, this combined with the SD card mod would let you simply plug in the router to your cigarette lighter and go, logging the networks to the sd card. It also isn't a hard mod to do. Depending on your GPS, this may be as simple as soldering 3 wires to your router. In my case it was a little more complicated, but by no means hard. It was just like adding a serial port, but instead of adding the serial port, I added the GPS.
See a picture or read here for more information.
A package for gpsd is available in Nico's test repository.
A HowTo for adding a GPS to the WRT54G http://www.frontiernet.net/~beakmyn/OpenWRT 20Kimset 20Server.htm