The Cambridge Autonomous Underwater Vehicle, built for the SAUC-E Challenge, is a fantastic example of UAV construction. The competition is to build a UAV that can complete an underwater assault course. This baby has a full computer inside it, based off of the worlds smallest full featured x86 motherboard, the Pico-Itx.  It has a 1GHz EPIA PX 1000 Board, 1 GB of RAM, Wireless Network capabilities and runs Ubuntu server 8.04.

The CUAV suffered from leaks which ultimately cost it the competition, but the information on the build is fantastic. They have detailed pages upon pages of information about the Mechanical, Electronic, and Software aspects of the design.  They even went back in and added notes from what they learned during the competition.  The project is also outlined in much shorter form on the mini-itx website.

[thanks Vesaines]