Curtains for sure, even if it's just panels on each side that may or may not cover the window when pulled shut. On the wall with multiple windows, just panels on the outer frame like this, they don't have to be functional, just softens the room:

Turn off the ceiling light and buy some lamps to soften the room. And, yes to rugs, pillows, curtains - anything to bring color into the room.

No cowhide--not at all in harmony with your furniture and paint choices. To pull the room together you need a rug in white, blues, and grays, the lighter the better since your floors and walls are so dark. (Is it possible to repaint the ceiling so it's all white?)

phuninthesun's top rug would be wonderful. Moroccan style rugs are soft, and often come in whites/creams and grays. Also consider creating a cozier conversational grouping by putting your white chairs at the ends of the coffee table so they face one another.

Curtains:

Pillows:

I'd like to see another accent color brought into the room - art that has more colors in it than just blue, white & gray, & 'things' on your shelving unit, or a rug with more colors. Coral or soft gold for instance. Your floor has warm tones so adding a warm color somewhere would look nice. The fact that you were looking at cowhide is a clue you might like to add a little warmth to the room.

Agree with mjconti: bring in some yellow, lime, or orange in small doses.

wondering why you didn't opt for the inset blinds instead of hanging them on the 'outside' ? (or is it just the photo angle?) The way you have them, looks unfinished. If you are keeping those, then get some light, billowy white drapes

A rug is a must. put a tall plant in the corner to the right of the white chairs.

I'm thinking a longer coffee table,,

idea for rug and accessories.

I could see a lighter rug with white curtains. Maybe you could do two coffee tables side by side? Larger table between the chairs.

Okay, looking again.

Swap out the tray on the coffee table for something funky and colorful - I love Pier 1 for stuff like that - and add some color to the things on the tray. The room as is looks very 'safe' and subdued. Not sure what your personality is... browse around TJ Maxx housewares, Home Goods, Pier 1, World Market, etc. and pick up a couple small things that make you smile/feel good. A pretty vase or box for for the top of those shelves (in a color not blue or gray), a tall plant or scuptural "thing" for that corner between chairs and couch. Go with colors that aren't the same as the wall, sofa or chair color. Keep receipts, bring them home and set them in place then live with them for a few days - make pictures and repost here, if you want... Return anything that really doesn't work in the space (go with your gut). ENJOY! Its your house.

Definitely go with a rug that has a simple pattern is predominantly light in color with the blue and gray PLUS other fun colors as well. Then you can pull rug colors to add pops of color/interest to the room. Have a look at FLOR carpet - you can customize your rug from size/dimensions to which colors you go with!

Also check World Market for a couple of POW (visual impact) ottomans. Get two! (The one looks like you ran out of ideas - 2 make an "I know what I'm doing" statement) pouf style ottomans come in a HUGE variety of colors/materials...

world market pouf - "Gold" accented cowhide

world market knitted pouf - multi

Just need to fill it out a bit! Here are some more ideas:

Large patterned area rug and pillows will do the trick...