Simple built-in to create a mudroom and/or storage anywhere from an entry, to kids room or in a laundry room by adding shelves or a deeper bench for sitting. Put drawers under bench or have the seat lift up to store things.
Old Window. A curio cabinet (or could be used as a medicine cabinet for the bathroom?) made from a repurposed window frame.
Best of DIY Home Decor: Everyone needs a broom closet; here the brooms, mops and cleaning supplies are very efficiently housed in a narrow pullout cabinet. Everything is handy and accessible, much easier to grab than from underneath the sink.