A space that's hardly ever used is behind the toekick of lower kitchen cabinets. You can make the space useable by having a good cabinetmaker craft you some toekick drawers.
They're about 3-4" in height and are literally stowed behind a cabinet's toekick. Good for storing away user's manuals, cookie sheets, and other flat items. It's storage you can add without changing the appearance of your place at all.