Those bulky paint color fan decks are a thing of the past. Benjamin Moore has a great virtual fan deck online! You can easily browse colors based on collection (e.g. historical) or just by general category (e.g. gray).
Bridget's post about gray walls lead me to the virtual fan deck. Check it out below. I think Winds Breath and Smokey Taupe are my favorites.
I also love the Canterbury sofa from Crate and Barrel that she posted about - the basketweave fabric has great texture and the shape of the couch is very classic. But with gray walls, the sofa would definitely need to be a different color. Maybe the blue? Or even the brown.
I'd spice up those muted colors with a bright rug and throw pillows.