This is one of my favorites. It is VERY easy, takes just minutes and looks great! Go to one of your local arts and crafts stores to pick up a canvas (already mounted on a wood frame) the same width as your bed. Next find a piece of wallpaper that you love - it only takes a small amount of wallpaper to cover so you might go to a paint store or interior decorator for left over pieces. Now simply glue (follow instructions for mounting your wallpaper) onto your canvas making sure to wrap the edges. And VOILA! It is light and easy to hang... the ultimate DIY project!
Another great idea is to build an upholstered headboard. Get a piece of plywood cut in the shape and size that you wish. Find a fabric of your choice and style to cover it - I would make sure it is an easy fabric to clean. At your local fabric store you can also find "batting" of different thickness to add some cushion and depth to your headboard. Now simply spray glue the batting to the plywood, wrap the fabric around the batting and staple to the back of the plywood. Add decorating touches with tacks (as shown) or buttons.
Same idea as above, but try using an arrangement of fabric covered squares or rectangles