We've seen modern come to lots of kids' spaces, including bedrooms, dollhouses, and furniture. So why not play houses?
Play Modern has created several designs for modern, sleek playhouses that might actually add to your decor, instead of detracting from it. With a modular system, there are many different configurations, all with clean lines and a modern sensibility. Sets are available for indoors and out, and various accessories all add to the aesthetic.
These houses aren't cheap, so if you are a DIYer, you might consider building one yourself.
Available through Play Modern.

Ercol Bar Stool
I actually laughed out loud for about 15 seconds straight when I saw the price of the bigger ones. That being said, they ARE pretty sweet.
Many of the images on their site show these outside. Unless you cover these in some pretty serious marine finish they are gonna bow and be destroyed in a year. Plywood gets water in it's ends and goes bad pretty quick. If you did a real good thick paint job and added some caulk and trim you could make these last longer.