There are a few different ways to get better Wi-Fi coverage throughout your home or office. A router should be able to cover at least 150 feet with Wi-Fi signal, but it could be less if there's a lot of interference from wiring in the walls or other devices. Simply moving the router to a new location could help.
Another thing to try is a Wi-Fi extender. Make sure that the extender is the same brand as your router so that it will be compatible. You can even use a second router in "bridge" mode to extend another router's signal.
If you're still having problems with Wi-Fi coverage, or just inconsistent Wi-Fi signal, you could try installing different firmware on it. DD-WRT and Tomato are two open source router firmware options that may be more reliable.
If none of these above steps are improving your Wi-Fi, it may be a problem with the router itself. Leo likes NetGear and D-Link routers. A more expensive but reliable option is Apple's Airport Extreme.
Sometimes Wi-Fi isn't the best option at all. Hard wiring with an ethernet cable will deliver a faster and more stable connection, which is essential for video conferencing for example. If you need to extend the network without a lot of additional wires, power line networking may be something to consider. This uses the existing wiring in your house to extend your network, and it's gotten much better in the past few years.