My theory is that if a book is useful to a writer, then it is useful to an avid reader. Most of them anyway. Here is a blog post at OnlineUniversities.com with a compiled list of 75 books of particular interest to writers. The blogger arranged the books into 9 categories which, of course, overlap somewhat: writing basics, advice from authors, improving your writing, grammar, references, writing as a career, genre or format specific, classics, and creativity and motivation.

It seems to be a good list. All of my spot-check selections were in the list: Stephen King, Orson Scott Card, Strunk & White (woe be it if that weren't there) and a couple others.