Dino Segovis from HackAWeek.com, has put an excellent tutorial on how to build your own DIY Amplifier for less than $20 with LM386 chip and parts bought from RadioShack.
As you can see in the video below, this 1/2 watt DIY amplifier is pretty powerful little amp, all encased in an altoids tin. This small amp even has a guitar jack and ability to distort sounds, pretty darn impressive for a small circuit.
I think this is a great, simple circuit for those of you who want to build your amps. In fact, I will have to try making this very amplifier soon.