Do any of ya'll collect/use reference materials?

The missus and I -- both writers -- have two shelves full of various writing reference materials: from time period, to plot/structure, crime references, to the occasional writing lifestyle book.

We've got most (if not all) of the "Elements of Fiction Writing" series from Writer's Digest Books, some of the "Science Fiction Writing Series."

Do any of you use these? If not, what do you use? Can you suggest other good reference materials? I'm not looking for a specific genre, really. I haven't bought a 'writing book' in what feels like an age, and wonder if there is anything out recently that would be a good reference, or even just a good "read."