Coffee can antenna
Here's the perfect can for a coffee can antenna. The proportions are nearly perfect:
http://www.caffecalabria.com/tins.html
Damn good coffee, too. I highly recommend the Calabria Blend.
I've built a couple of these.
Get a USB wifi adapter that has an antenna connector - the Alfa brand is excellent and inexpensive. The wifi adapter is small enough to just plug directly into the connector on the coffee can. This avoids a coax cable and resultant cable loss. You can use a reasonably long USB cable and it will work fine, without the signal loss from a long coax cable.
Forget about Pringles cans - they are bunk - the inside of the Pringles can is NOT metalic.
Use the basic "Yuban" design, but use an online calculator to determine the feed-point for the Cafe Calabria can (or similar-sized can.) The longer, skinner can will work better than a fat Yuban can.
I epoxied a nut to the side of the can, so that it can be mounted on a mini camera tripod.
I drilled a hole in the can for the female N connector that you solder the feed wire to. I picked up a metal SMA to N adapter (NOT a cable, but a solid adapter.) That way, the wifi adapter just hangs off the side of the can.
Here's the wifi adapter. Actually, it will probably do a pretty good job without the cantenna. I took my cantenna out on the balcony and can pick up 200+ signals from around the neighborhood and as far away as across San Diego Bay, a couple of miles. They have a number of models, ranging up to 2W power. I haven't heard good things about the 2W model, though. Stick with 1W or the 500mW model that I used.
http://www.amazon.com/Alfa-802-11b-Wireless-Original-9dBi/d/B001O9X9EU
And a couple of articles on antenna construction:
http://www.turnpoint.net/wireless/has.html
http://www.oreillynet.com/etel/blog/2002/02/the_essence_of_community_wirel.html