here are some other options:
Wall-Mounted Storage: Towel racks, shelving, and wall-mounted cabinets all provide storage space without a large footprint. This polished nickel shelf with hooks is $99 at Amazon. For more wall-mounted storage options (including the shelving shown in the top photo), see this post.
Over-Sink Storage: The standard solution for over-sink storage is the medicine cabinet, but there are other options as well. Open shelving, wall-mounted cabinets, and wall-mounted racks are just a few things that can replace the shallow storage space of the medicine cabinet. Use a wall-mounted extension mirror so that you'll still have a vanity spot in the bathroom. Restoration Hardware has a good selection of extension mirrors, including this Sutton Mirror currently on sale for $63.99.
Under-Sink Storage: If you have a sink with built-in cabinet storage, you can use stacking shelves to increase the amount of storage space. Even if you have a pedestal sink, you can find under-sink shelving like this chrome shelf from SkyMall for $29.99. If you want to cover the shelves, you could sew a curtain to fit the area and use velcro to attach it to the sink.
Shower Storage: Shower caddies are great space savers in the bathroom. This adjustable shower caddy from simplehuman ($39.99) has multiple storage compartments, holders for upside-down bottles, and adjustable shelves.
Over-Toilet Storage: The etagere is a classic small-space bathroom solution. This Apothecary Etagere from Pottery Barn is $549, but other versions can be found for less. We also like the Hudson Chrome Etagere at Stacks and Stacks for $115.
Window Storage: If you have a small window in the bathroom, install glass shelving to let in light while adding extra storage space. This bathroom from Coastal Living has lots of light with storage space. If privacy is an issue and you need to screen the window, use an adhesive window film behind the shelves.
Free-Standing Storage: If you have any extra floor space in the bathroom, free-standing storage can work well. A ladder rack has a small footprint. This is the trellis leaning towel rack from Umbra, $63. We also like the Componobili Unit for a bathroom. Any other ideas for creating more storage space in the bathroom? Top Photo: Zen Bathroom from the Container Store