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.