The question is: "Do you need Omni directional Coverage?
If the answer is yes, Antenna is probably Not your solution.
However, you keep insisting so this might help,
http://www.fab-corp.com/home.php?cat=282
If the answer is No, High Gain Directional Antenna is the answer,
http://www.fab-corp.com/product.php?productid=1438&cat=255&page=1
The Real McCoy is,
Method One (The best). Lay few CAT6 cables to central locations in the house, install Access Points, or Cable/DSL Routers configured as Access Points (
Using a Wireless Cable/DSL Router as a Switch with an Access Point
Method Two (No Wires). Get a high power Buffalo Wireless Router.
http://www.newegg.com/Product/Product.asp?Item=N82E16833162134
If you already have a good Wireless Router installed you can skip the above and Start here.
Install Netstumbler on a Laptop, and survey the house the Laptop with Netstumbler,
http://www.netstumbler.com/downloads/
According to the Netstumbler?s signal strength reading, identify spots that have strong signal, and spots with weak, or No signal.
Additional Wireless Routers in WDS Mode (
Wireless Network - Configuration Modes.) has to be placed in spots were the signal is good about Half way to the dead spots.
Buy (one at the time) BuffaloTech Wireless Routers, configure them as a WDS units to the Central High power Router.
http://www.newegg.com/Product/Product.asp?Item=N82E16833162173
How many units? It depends on your specific environment that is the reason of buying WDS units one at the time, try it, and decide on the Next step).
There is also an option to flash the Buffalo units with 3rd party firmware to augment functionality.