Covering your walls with artwork is a great way of spicing up bland walls.
For example, photo boards make a great addition to your room. Not only do they add color and interest, but they connect you to important people and places. They can be made from cork board or can be covered with material that coordinates with your room, as seen below (picture 1).
Another option is to buy pre-made canvases, or paint your own! This, too, can be seen below (picture 2). Tapestries are also very popular.