From Mi Llave Allen, here's a clever way to fit quite a bit of shoe storage into a small space — smaller Lack shelves, hung at a diagonal for maximum efficiency. - 11 Ways to Use IKEA's Lack Shelves in Every Room of the House
A slim floating bookcase is a nice, clean way to add storage to dead space. In other words, make your dead space COME ALIVE. Get the directions here on how to turn an Ikea bookshelf into a floating one.