Take a ladder shelf and left out the bottom 2 rows to fit perfectly over the toilet. This could make for extra storage space without looking too bulky. http://hative.com/over-the-toilet-storage-ideas-for-extra-space/
OVER TOILET STORAGE (Item #30260) | review | Kaboodle This is pretty nice although it would make toilet maintenance difficult. You'd have to move the shelf to access the flush valve assembly inside the tank.