If you want to add storage space to your bathroom, you have basically two options: adding a stand-alone floor-standing piece of furniture, or mounting a shelving unit to the wall. Both will provide you with shelving that you can use for bath products, toiletries and small towels. The advantage of the floor-standing models is that there is no mounting involved. You may have to do some assembling though, depending on the model.
I like the simple look of both of these, and I especially like the curved detail on the white one:
Over-the-toilet storage units:
Over-the-toilet storage pictured:
Left: Zenith Products 9107W Country Cottage Etagere Over-the-Toilet Shelving System, White
Right: Zenith Products Espresso Wood Moderne Frosted Glass Window Spacesaver