Best way to extend Airport Extreme signal

Like most folks, I had no idea what a poor choice it was to let my internet service providor install my DSL connection in the far corner of my home. So until I install a phone or cable jack in the middle of my place, half my signal is wasted in the back yard, while the other end of my house is out of range.

(iPad 2, iPhone 4S, Macbook, etc)

My question is... what's the best way to extend my Airport Extreme wireless signal? I tried using my Airport Express as an extender but recently read that this actually weakens the signal. If that's wrong, how should I configure them to work?

Does anyone know of a better way to extend my wireless signal to the rest of my house? Short of moving my router?

Thanks in advance!