I do love a good steel and plate glass window. There's something about the industrial/factory feel and the amount of light that filters through that I gravitate towards. And while I love a great structural steel window wall between indoors and out, I think they make equally amazing interior dividers. Keeping the light flow consistent throughout multiply spaces while creating necessary sound or visual boundaries.
Oh for this to be at the end of my tiny kitchen. Steel french doors leading out to a tree-filled courtyard. It's the stuff of dreams, I tell you!
I also love the use of a window between the kitchen and dining area in Nate Berkus' townhouse kitchen. It keeps this city kitchen, which all to often can seem dark and cramped, bright and accessible when entertaining while still maintaining a bit of separation when needed.