Tone Block
The combination of a heavily chambered guitar body with extra mass at the bridge, results in more vibrations throughout the instrument. This imparts a kind of haptic feedback effect that you can feel when fretting notes or strumming chords, as well as more low-end rumble.
The Tone-Block gets drilled and tapped for the bridge screws, tying the bridge and block together tightly.
While I make no claims about the final sound of the instrument through an amp, I find this subtle coloring of the feel of the guitar was enough for me to pursue this feature multiple times, and I have been overjoyed with the results. I find myself missing this aspect of instruments that are built without it, and my customers have been loving it as well.
This combination can be added to any non-tremolo custom build for $400.