Power Over Ethernet (a.k.a. PoE)
Using the extra wires in a CAT5 cable to carry DC to a device such as an AccessPoint.
Links
TerrySchmidt has a great description of PoE on NycWireless along with plans for building your own. http://www.nycwireless.net/poe/
Andy Freeman from http://geelong.wireless.org.au has made a Power over Ethernet module to suit a 5.25inch drive bay. http://kawasaki.kz/wireless/poe.htm
Several vendors are starting to sell ghetto POE solutions quite cheaply.