I've used a few different antennas to boost WiFi
range. I usually get them on a magnetic mount base. The ones that were specified as 6db or 8db boost gave me about twice the original range realistically. I also have a 90 degree directional antenna
from Hawking that is specified as 15db gain. It gave me about 4 times the original range, but it had to be pointed in the right direction. I think that only about 60 degrees actually gave good performance.
Boosters are OK of you have a place to station them between you & the original signal. They work best when they are near the half way point. A 100 yard hard wire run to a second access point seems to give better coverage than most repeaters. Some of the repeaters don't need any real configuration to work with open signals.
There is a lot of hardware
out there these days. Some of it is programmable to the point where a single
$40 device can be an access point, a bridge, a repeater or a router. Fry's electronics
(frys.com) is my favorite source due to selection available, but you can even get some of things from Office Max or Staples.