Today I installed a cantenna on the roof of my apartment building. A "cantenna" is a highly directional, high-gain microwave antenna made out of a can, like a soup can. The most common application is for long distance wireless internet links (802.11x). I made my cantenna out of an old Maxwell House coffee can.
The cantenna points towards the UCSD Cancer Center, which is roughly 325 meters away from my apartment. This is outside the usual range for wireless internet. My apartment faces Southeast, while the center is Northwest of my building, meaning I cannot see the building at all from inside my apartment.
After getting permission from the apartment maintainence supervisor, I put a 16" long peice of 3/4" square pipe on the facia of the building. On top of that I screwed on an old flag mount, one you would attach to the side of your house on independence day. The flag mount has a part that has one pi steradian movement, allowing me to have a good measure of freedom to aim the cantenna. The cantenna is wired to a Linksys WET11 which lives in a plastic box under the cover of my porch ceiling. From there an ethernet wire goes inside through a small hole in the screen door frame.
It was amazing how easy it was to get a strong connection! I had already done some simple tests, holding the cantenna up on the end of a broom. But nothing was guaranteed until I actually installed the thing. All I have to do is make sure the trees stay pruned back!
While it isn't the fastest connection ever (~300 kb/s max) it is very cheap (free-99). I estimate I've put about $100 into materials. My own DSL/Cable connection would cost that much every two or three months. It's especially fast to campus computers, where I send most of my data back and forth.