a painting and a narrow table under.

A large painting or tapestry to cover completely. I little too shrineish for me.

Create texture as a backdrop and put in vase/flowers, sculpture, painting, or put up a small wall mural depicting a scene.

I think a sculpture or a sculptural vase would look nice there. A "Flat" vase on stand for fresh flowers. Or, you could fill with lavender. Lavender lasts a long time and smells nice.
Just be sure the size complements the opening.

Items to consider that you can find online:
An antique camel saddlebag
An antique brass tray
An interesting mirror
A large Italian ceramic platter
A collection of antique copper molds
A collection of old keys or any other collectible you like.

I suggest you tour around an antique store with an open mind.

Hire someone to do a trompe l'oeil mural in the niche reflecting the style of your home or your taste in art! :)

Here is a nice piece which may work if you like it.
http://www.amazon.com/Cressida-Glassware-Signature-Machinery-Abstract/dp/B007RB54LK/ref=sr_1_19?s=home-garden&ie=UTF8&qid=1389467915&sr=1-19&keywords=vase+stands

Try a mirror - either round or with a rounded top edge so that it fits with upper curve of niche and add a small ledge or skinny console for keys, flowers, etc. Some mirror ideas attached

It would have to be a large piece to "own" the space. If your budget will stretch that far, how about a piece of antiquity in bas relief? - but you would have to get the lighting just right,

Here are a couple more mirror ideas

Nice size and great price, Darz!

The Juno console in cocoa from Bryght would make a great addition to your foyer... add a few decorative personal treasures and a table lamp and it would make for a warm welcome to new guests. The Strip desk in ebony would also work really well with your color scheme, add some stylish table décor and perhaps a colorful piece of artwork and you're done! Just a thought. For more styles and information www.bryght.com

A demilune table would work better than a rectangle. I would be forever banging into the corners with my hips, LOL! Smaller than this one of course...

Hire a mosaic artist to do a custom piece to fit it. Here is someone http://www.lauradinello.com/

I agree, hire an artist. I love niche threads. Long live the niche!!

It's nice to have a light in the top of the niche to enhance your artwork or orchid, etc. Go the TJMaxx and pick up some pretty glass vase or sculpture to pick up the light. There are so many inexpensive and beautiful glass pieces on the market. Or if you have a family treasure or "conversation starter," use the niche to set it apart. I love niches. The nice thing is, anything you put there isn't permanent.

Drywall over the niche and then you're completely free to hang a picutre, mirror or whatever. Not a fan of the niche. At least yours isn't too big and if you like it--do a painting with an arched frame.

You could also put molding around the arch and add wood shutters and pretend it's a small window like the pic on the right. A light behind shutters would look subtle with them closed.

Or add shelves and molding to make it more versatile.

I added a mosaic mural into the niche for an example

http://www.Mosaicsyourway.com

pretty!!

An orchid, living or silk. At least you can change it seasonally or if you grow tired of it. (The wallpaper in your foyer is amazing!)

A black and white photo... fun family related! or keep it open till you find something interesting while traveling.

I would put the wallpaper from the entry in there to start and trim it off. Then have a good think. The ledge area is very narrow and there does not appear to be lighting incorporated. You can get inserts for it or have one custom made . Personally, I don't feel a fah fah niche fits with your decor. http://www.vintagewoodworks.com/poly-wall-niches.html

So, the idea of a niche is to highlight something normally as a 3 dimensional art piece. This starts to get very personal. It will be reflected in your design choices throughout your home. I would go with something figural and unique. Something that amuses, entices, excites you but mostly reminds you who you are.

Alternatively, you can grab anything, such as a handful of wheat bind it in a decorative ring and suspend it in there. Meaning, unless wheat has some special significance to you it will become a thing ...like anything else.

Added: You can also close it off with doors and use it as a drop place for things such as keys, and pocket items. Perhaps even building in a cabinet below it in the same fashion.

I had two in my home. Had contractor come and cover over with drywall and painted.

That wall is a great spot for art, but the niche itself seems to overly constrain the size and format of the art you can use, as well as rendering it busier. Also, this niche, like so many of them (this is a common dilemma!), seems a bit random in placement and stylistically unrelated to other trim in the house. I'd recommend drywalling it and painting it (i.e. remove the niche). Then you have the freedom to choose art in any format, or even leave the wall blank for a more restful look.

Consider a large hurricane sconce (either candle or wired) with console (1/2 circle) below. Adds dimension, function and welcoming sight for visitors. Altho I'm not a fan of niches, I think in your home it adds some softness to the angles and rectangular windows and repeats the arched entrance to room on right.

This is a beautiful foyer!

WOW! Mark, I love the smokey mirror with the design paint on it. Maybe Toyin could have the pattern from her wallpaper painted on a smokey mirror. Then she could place a candle there to reflect the light. I'm inspired!

The smoky mirror with the wallpaper stenciling is pure genius. Kudos Mark. I would be more apt to put a led candle in there then a real one though.

Mark, what are those "buttons" on the mirror? Do they fasten the mirror to the wall? And what kind of paint would you use to paint on glass that would be durable? :))

Thank you for all the input