Note that many of these antennas (like the pringle's cantenna) create high signal gain in one direction while killing antenna range in all other directions. That is, you point the antenna in the direction of other other device. This is fine if all your WiFi computers are close together at one end of the house and the wireless router is at the other end of thehouse. But, if the computers are all over, a high gain antenna could kill reception at all the computers except the one the antenna is pointing at.

If you need omni-directional gain. Try a monopole or collinear antenna. Maybe this one would work:
http://www.geocities.com/lincomatic/collinear.html

If these antennas look like too much hassle, then look into how you can relocate the router or the computer for better reception. The two biggest problems with wifi reception come from: 1) conductive materials sitting between the computer and the router (duct-work, piping, metal furniture, and people) and 2) other RF devices in the same frequency band (cordless phones and microwave ovens).

Good luck!

G4From128k