Built-in cabinets. You build the structure like a box, but the face piece goes on front to define the cabinet/drawer openings:
I was considering MDF for two reasons. One, i plan on painting the unit, not staining it. Two, cost. Have you seen what a 4x8 sheet of carpentry quality plywood costs these days? (not to mention how much pine 1-by it would take to build shelves on an 18' wall...)