I'm creating a TARDIS door that plays a sound when you open it. It's working, but not loud. I just picked up this amplifier from dx.com, but I'm not sure if I've added it correctly. It is louder, but I was hoping for more. It's mono, so I've just hooked the speaker up to the "L OUT + and -". The other + and - are to my power rails (feeding from USB power source for now). And the "L" in the group of 3 is connected to my speaker out from my audio board. Does this seem right? What is the weird symbol between the "L" and "R" in the group of 3?
What is the weird symbol between the "L" and "R" in the group of 3?
It is a symbol for a common signal ground. The one of the stereo inputs goes between this pin and R and another between that symbol and L.
http://www.diodes.com/datasheets/PAM8403H.pdf
3W with 4 ohm speaker.
http://www.mpja.com/4-Ohm-Mini-Speaker/productinfo/14618%20SP/
This one in decent enclosure would give you good volume.
USB is limited to 5V, 500mA, so that's only 2.5W to start.
I should have figured.out the stereo thing. 
Thanks, I'll keep those parts in mind, if my door isn't loud enough when I put it in place.
The chip is what's on your board already, the only change really is to a 4 ohm speaker.