If you are not looking to refinish, painting the brick could look really nice. However, if you do not wish to paint it or re-face it, I would have the ledge covered with a chunky wood to look like a floating mantle. But nothing too dainty, as it quite large! If your budget is a little more friendly, but not large, you could do the above, but have the bottom re-faced to pull off a more custom look. Maybe a larger stone tile of sorts.

How about Whitewashing the brick? And or adding some crown molding for a more dramatic look.. http://www.thepainteddrawer.com/2013/12/whitewashed-brick.html

Here is an example of crown molding