Living with plain walls can get boring! The good news is there are several easy ways to add color and impact to your walls without too much labor or cost. You can use lightweight wall board or a art canvas, then paint it any color you like. They are quite easy to hang and you can take them with you when you move. Also, a way to add huge impact and is to find a graphic or print fabric that you love and use a staple gun to fasten it to a canvas frame or a lightweight board. If you want a soft padded look you can use batting beneath the fabric. Be sure to pull the fabric firm around the edges of your frame and staple on the back so you don't see fabric edges. This same technique can be used to create an inexpensive custom headboard.
With fabric that has a finished edge, a very inexpensive way to hang it is by putting a wood dowel at the top to hang it from and another at the bottom to weight the fabric down. I recommend using iron on adhesive to create a pocket at both the top and bottom of your fabric to slide in the dowels. You can find dowels at most craft stores and at Home Depot or Lowes. For bargain fabrics, check the remnant section of your local notions store. Have fun and get creative.
(photo sources: pinkpaperpeonies.tumblr, roomu.net)