The Best Books on Writing You'll Ever Read
The bottom line is this: Good writers read. If you want to become a better writer and you're not reading books and articles all the time, then you don't really want to become a better writer.
I've said it before and I'll say it again: Good writers read. If you want to become better at your craft and you're not reading often, then you aren't serious about improving.

Sorry.
The bottom line is this: Good writing comes from good reading. But someone can read a statement like that and get the wrong idea.
Not all books are created equal
If you can help it, don't just read anything. You should spend your time reading the best books you can find. There is, after all, a lot of junk out there.
That said, I wouldn't worry too much about reading the right books. Just get started. The act of reading anything (even romance novels) in and of itself will make you a better writer. I just want you to make the most of your reading time.
If you're pinched for time, I recommend finding a good book list and going through it. You only have so many hours, and you want to spend them well.
So, let's compile a reading list
Becoming a better writer isn't just about learning grammar and and syntax. It's not just about practice, either. It's about becoming a well-rounded communicator — someone who knows the rules and understands how to break them.
So, without further ado, here are some of the best books on writing that I could come up with (after asking some friends):
On Writing by Stephen King
Walking on Water: Reflections on Faith and Art by Madeleine L'Engle
A Million Miles in a Thousand Years by Donald Miller
The AP Styleboook (for reference)
The Artist's Way by Julia Cameron
The War of Art by Steven Pressfield
Bird by Bird by Anne Lamott
On Writing Well by William Zinsser
Eats, Shoots, & Leaves by Lynne Truss
The Writing Life by Annie Dillard
What would you add to the list?
Recommended reading: The 10 Best Books About Writing [Paste Magazine]
*Disclosure: The above links are affiliate links.