You can also use the aluminum L bracket used to hang suspended ceilings it is used around the perimeter of the room. Cheap and easy to cut but may have to be spray painted to your desired color.
+1. This is what i used and it looks great.
Be sure to have a good pair of tin-snips / metal-shears for cutting the angles, they make the difference between a clean 45-degree and an ugly one. Buy a full length, that will give you enough to do it twice, best for Trial-and-Error.