The idea of using an amplification chamber to boost audio volume passively isn't exactly new, but this monster iPhone Bugle Horn just might be my favorite to date. Some other passive iPhone speakers include the Griffin AirCurve, the Horn Stand, and the Horn Bike.
The iPhone Bugle Horn Speaker uses a natural horn shape to boost the acoustics of your iPhon’e's tiny speaker. They even left a cut-out that allows you to continue using your charger. Yours for about $32 here.