Another thing to consider is the antenna on the router. Most antennas that come with the router are very low gain and omnidirectional. You can get high gain omnidirectional antennas at places like Frys for not too much money. These will extend the signal farther by increasing the signal strength.

You can also get a very high gain directional antenna for a router. But you will need to be within a narrower coverage area with the antenna pointed in your general direction. The good thing about a directional antenna is that it won't pick up much signal from the sides or the back, or top and bottom, so if positioned properly you can eliminate a lot of the signals coming from your neighbors. In the direction which it points, it will produce a high signal strength because it is focusing the signal in one direction rather than all around.