How deep is that ledge?

About a foot

I would suggest a high impact piece of art in the middle and a couple of vases of different heights at either side

This is the best picture I could find (I think the stuff is ugly, but it demonstrates the high and low). You could even do a gallery wall instead since its such a big space.

Great idea, Thank you!

Great art and that's all you'll need

The picture Margo sent is a great illustration. Adding wood or any other type of surface material will transform that niche into an architectural detail which will set the tone for the rest of your interior. Not that adding art or a mirror won't look fine, but by introducing a new material first, you'll get a lot more bang for the buck. If you like a formal look you can consider polished stone or granite, wood or mirror. If you prefer more casual you might use distressed wood, matte tile, or hammered metal.

Put metallic or chalkboard paint on the area. Then you can have a couple vases on one side and a basket on the other. (The basket could have chalk inside.) You could also hang a masterpiece or some gallery type thing of paintings. :)

Thank you everyone!

Think outside the box:

LOL- grover- this is another case of two heads are not always better than one;))

15 or 20 heads are way better than two, though.

How about heads and tails;)