If your home or office Wi-Fi isn't performing well you might consider improving the signal using an electrical powerline extender. Many larger homes and buildings are likely to have dead spots where you can't receive a Wi-Fi signal from the router due to walls or distance from the router. Netgear, D-Link & Monster all make WiFi powerline network adapters that you should consider below. This technique requires two WiFi routers and will work with Airport, Netgear, Linksys, D-Link WiFi routers.
How does it work? Powerline extenders send a WiFi signal over the electrical powerline, instead of over an Ethernet cable. Simply, plug one powerline extender into your router and another into a power socket in a poorly covered area of your homes or office. However, you need to make sure that you both extenders are on on the same circuit, otherwise it will not work. In this case you can use an Ethernet to bridge circuits between adapters if they're not too far apart. Keep in mind you can have multiple powerline networks plugged into the same electrical circuit and do not plug into power-strips. If you want a further technical explanation of the technology read the Arstechnica Wifi networking article.