I have two thoughts. 1) Something old, tribal, and hand knotted as a contrast to the modern lines of everthing else to add color, pattern, and texture. 2) Don't buy a new rug and spend the money on a killer piece of artwork for above the mantle, and some new pillows for a punch of intense color.

How about leaving the existing carpet and painting the walls? Paint is cheaper and would make a bigger impact. Then add some new throw pillows and some plants...

It's a question without an answer. Are you going to paint the walls? Are you going to change any of the furniture? Right now the room is kind of blank - a rug might be the most affordable way of adding color, but is it the best way to start?

Your room is so neutral, almost any rug will work.
Then pick up a predominant color in your rug, and use for accent pieces, pictures, pillows, that sort of thing.

I agree with @ISHWARKE - paint the walls if you can. I also like the idea of a tribal rug. Painting the walls is cheaper.

Paint.

Or pick a nice bright color and some funky art.

I would go with some vivid tribal rug because that's what I like. But it really depends on your preferences. Are you ok to live with patterned rug in bold colours for a couple of years or do you prefer to change the colours often? If the latter, keep the existing rug, paing the walls and add additional colours via cushions and other accessories.
Vere nice place, BTW.

Cowhide rug

An old Persion rug would look amazing (they look great almost anywhere). They add warmth, colour, comfort, style...

I agree with those who suggest a vivid tribal rug. A more traditional oriental carpet in deep red tones or would do nicely too. You can often find them on Craigslist. An alternative to strong color in the rug would be adding one with little color, but lots of texture, like a white flokati, or a neutral hile-pile rug of some kind. Your house is so nice!!

pint the walls, its cheaper.

Or go with an orange rug

I don't know why, since you asked about the rug, but I am picturing a large grouping of oversized, brightly-coloured glass on the mantle, maybe tall vases of different heights or something. (I'm seeing cobalt and red, but you probably have your own faves, lol.) And maybe some colourful artwork that you love. I think the rug is fine, and making the fireplace into a focal point with colourful accessories would perk up the room and give you a quick way to bring in colour....then take your time to decide where else you want it. This is a lovely room! There are lots of ways to go to add colour. For me, I don't know if a rug would be one of them, as it would pull the eye immediately downward instead of around the expanse of that lovely, airy room.

What about wallpapering the mantle?

Also, I love your sofa. Would you mind telling me where you got it?

Any you love. But figure out what vibe you want from the room first... calm? funky? collected? quiet?

But if you want to keep things neutral, you need a rug with some serious texture.

How about something from FLOR? There are so many options in color, patterns, textures, and piles.

I like the serene look of your room. Perhaps you would like a black rug? It would echo the fireplace & speakers, and anchor the room. The pale rug feels as though it is floating, not holding things together. An organic (cowhide) or rounded shape would contrast with the soft angles you have.

An Angela Adams rug. or maybe a flokati rug. I also like the idea that people stated above as to the tribal rug.

You have such a blank slate here, so you can really add any color to this room depending on what your style is and where you want to go. I've read several other posts arguing paint vs rug. I'd start with the rug and coordinate with pillows to brighten things up. And you don't need to spend a lot - Ikea, West Elm and Cb2 have some really great budget friendly
rugs.

Love the FLOR idea posted above too!

I would definitely check out craigslist nice rugs to be found. I bought a rug from rugs usa and was very pleased. I wished I had known about it before spending lots of cash on all my other rugs.They have a tons of choices and random 50% sales and I think it was free shipping. heres the link and a rug idea
http://www.rugsusa.com/rugsusa/rugs/milliken-ahvas/toffee/279740755-1090132.html

When considering color, think about what kind of mood you want to create: cool, serene, warm, energizing, funky, modern, traditional, etc.

Me, I'd inject some color in that room with a nice bright hue. Another thought is to use the existing rug you have and paint a pattern onto it with a vivid color. Use stencils or make one... there's plenty of info out there on how to do it.

Or you could add a pattern to it with a more matching color. I'd just make sure it's a pattern than fits nicely with the others in the room (maybe something larger)?

I would go with a tribal Persian rug --- a Hamedan or Shiraz. The room is pretty classic, so a Persian would seem is in keeping with your sensibility. It will also not conflict with any art you may choose to put up in the future. They are amazingly resistant to dirt and wear and tear if you happen to have pets. They also will age much better than some rugs out there with contemporary patterns.

A crazy shape! High contrast! Something! This room is much nicer than any in my house, but it is SO neutral. It's like a politician who studiously avoids saying anything in particular.

I like the rug you have. Something bright there would draw eye attention down, when you have that fabulous fireplace up. I'd put something eye-catching that way, and maybe one or two throw pillows or something noticeable on the coffee table...

It's a really nice space.

If you don't care about that rug at all, I would paint some big yellow stripes or chevrons or maybe some irregularly shaped polka dots on it. Some non-matchy-matchy yellow patterned throw pillows on the sofa and chair and a big vase of forsythia on your mantle and you'd get a collected but not overly matching look. You could even carry the yellow into the dining room on the table to connect the spaces together. I say yellow because I am grooving on the yellow and grey trend right now, but you could switch that for pretty much any other bright color you like and it would look great. Sea green, cobalt, poppy red.

I'd like to echo with where cdeaton is coming from - if you planned on getting rid of the old rug why not just update it with some color? If large patterns aren't your thing, maybe start with just a border around the rug. It'll give you a taste of color and maybe help direct where you'd like to go with the rest of the room. Blues and Neutral/Browns were meant to go together.
My picks: turquoise or tiffany blue trim along the rug with something shiny on or over the mantle like a starburst mirror. You could add a throw to the chair or sofa to continue the color scheme.
Good Luck! Happy Decorating :)

I vote for a shag - preferable in white or off white. Maybe too predictable or boring but I like it that way !! Add some great art above the couch and punches of complementary colour in cushions and accessories.

I'm loving tribals right now, too, but your home doesn't say tribal to me. You have beautiful neutral pieces but the room lacks a little depth. How about some luxe neutrals and playing with texture and pattern? You seem to be going in that direction with your furniture and pillows. I can't quite see the pattern and color of the pillows, but I'm thinking something like:
West Elm Marquis Rug
West Elm Ikat Links rug
Crate and Barrel Belize Graphite Rug
Target Home Medallion Rug

and then for accessories do some subtle shine, light reflective or metallics but still neutrals like:

West Elm Recycled Glass Bud Vases
West Elm Gem Mirror
Crate and Barrel Deidre Vases

That kind of stuff can bring light and texture and warmth without taking you too far out of your neutral comfort zone.