Elements of Style
Yeah, that one.
Other books I have--
101 Habits of Highly Successful Novelists--This one has snippets and quotes from lots of different authors on different topics like procrastination, ideas, agents, editing, etc.
Zen in the Art of Writing by Ray Bradbury--Collection of essays Bradbury wrote about how he writes, and some are just reflective about what he's written, like one looking back at writing Fahrenheit 451.
A book by Terry Brooks, similar to the one by Bradbury
A book with lots of questions and answers by Janet Evanovitch. Haven't read it completely, but skimming through looks like a lot of it was taken from the FAQs on her website, with maybe some extra stuff.
Others that I haven't read yet--Danse Macabre by Stephen King, Self-Editing for Fiction Writers(though I don't know that this one will be helpful for me, skimming it, it looks like a lot of what I learned in writing classes), On writing Horror, On writing Mystery--both Writer's Digest Books, Orson Scott Card's book about writing science fiction, a Writer's Digest thing about writing science fiction/fantasy--it excerpts Scott Card's book, and has some stuff from Terry Brooks, I think, and Time to Write. The last I haven't read because I've been too busy writing, and most recently reading through the draft to revise.
Most of my stuff tends to lean towards speculative fiction cause that's what I write, and I get more out of essays and such than most How-tos. I might have some other books, but at least a couple of them I stopped reading because I found them less than useful.