While we normally look at the footprint of a space to find more room, when space is tight, don't forget to look up. If you're lucky enough to have an upstairs, Gregory pointed out that you can use that space above the stairs for display or storage. If you've got high ceilings, (and even if you don't) use the walls above a desk, in a hallway, or above the toilet for a set of streamlined shelves that can hold boxes with projects, books, supplies or framed artwork. If you keep what's on the open shelves streamlined and color coordinated it won't add to the visual clutter of a small space, it will become a part of the decor, like the picture above. West Elm and Ikea both have floating shelves that can hold up to 30 lbs.
Don't forget about conventionally kitchen related storage and organization ideas for a home office. This is the Asker Series from Ikea used to free up some counter space in an office. Could be great in a bathroom to hold makeup brushes and qtips or whatever else you like to keep out. A great example of using the walls to organize and keep things organized and contained.