Chris Anderson has put together a site for DIY Drones:
This is a resource for all things about amateur Unmanned Aerial Vehicles (UAVs): How-to’s, links, videos, images and a discussion group.
Among other things, this is where we’ll be listing all the parts, software and instructions to build each of our UAVs.
In my copious spare time I may have to give this a try:
GeoCrawler 2 (Based on a Lego Mindstorms autopilot. Less than $1,000 — start with this one)