I enjoy architecture and industrial design. It's a whole other discipline but one that should never be foreign to the concept artist.
How can you not love it? It speaks to us in volumes and forms, and compositional mass. I don't know a lot about it, I don't have the background or education, but I can certainly deduce a lot just by looking. That's half the battle really. I walk around a lot of the times asking myself questions: "Why would they have done it that way?" "Was it because of the materials available at the time? The designer's personal style? Was it the era in which the thing was built, a direct reflection of the times? Or was it an engineering choice based upon necessary function?
And while I'm talking to myself in public, I also answer in third person.
I once read a couple of books from Dover Press The Diderot Pictorial Encyclopedia of Trades and Industry. For someone who wants to understand the basis for many of our more complex processes in manufacturing and industry, I'd check them out. The simplicistic nature of the birth of machination and industrial design during the Age of Enlightment helped me to understand how many things work. Even if I don't get the details right, it's enough to push me to create convincing machines and environs.
Because really half the job of designing is to make something look believably functional. Otherwise you get nothing but cool fluff...and really who needs more of that?