Turn of the century end cap style
If your return vent is on the wall right at floor level and you want a metal piece, then these are a great way to go. We fold over the top and edges to form box. We can make the projection whatever you want, but typically it is either 3/4 inch or one inch. There are 18 different patterns to choose from and 6 finishes. They are provided with color matched screws. These are also available for locations that are not in between baseboards such as floor, wall, or ceiling. See those here.