For all that the craft parts of this book are some of the best I've read (4-5 stars), they're so outweighed by unrelated bits and pieces that I can only give this, as a craft book, 3 stars.
The Elements of Style,
by William Strunk Jr. and E.B. White
If you're a writer and you haven't read this, then drop your pen right now and pick up a copy of this book.
It's the definitive guide on writing decent prose.
You don't have to agree with these guys, but you
need to at least know what their standards are.
(King makes reference to this book a lot.)
Bird By Bird, by Anne Lamott
A similar vein of books-on-the-writer's-life.
(This one wasn't for me, but mainly because I
didn't agree much with her opinions -- she's
clearly speaking for a more "literary" writer.)
Lamott weaves her writing into her personal
accounts much more seamlessly than King does.
If you're looking for something more along the
lines of a literary-themed memoir (which I
clearly was not when I read On Writing),
then you should pick this one up.
It's a warm little love letter to every
aspect of bibliophilia, with sections on
everything from rearranging your library
to collecting obscure vocab. Very enjoyable.