We're pretty impressed by Landscape Structures' Mobius Climber, which can help kids get exercise and maybe teach them a thing or two about fourth-dimensional wormholes.
But what we'd really like to see is an M.C.-Escher-designed condominium with space-saving anti-gravity staircases.
Early architectural tests indicate it would work! Well, at least in Lego.
sources: 1, 2, 3