Stephen King - On Writing.
Interesting both for the autobiographical section and the practical section, even if you're not a fan of his genre.
Anne Lamott - Bird By Bird.
Thoughts on writing. She's more self effacing/less New Age-y than either Julia Cameron or Natalie Goldberg, and therefore appeals to me far more.
Robert McKee - Story.
Yes, he's a bit pompous and arrogant, yes, Story is often over complicated given he's basically writing about 3 Act Structure. But it's still essential reading in my opinion, especially good on sub-text.
William Strunk & EB White - The Elements of Style.
Succinct, precise, clear, short. The best £5 you'll spend, miles better than Eats Shoots and Leaves.
Renni Browne and Dave King - Self Editing for Fiction Writers.
Excellent book that does what it says on the cover. Good, clear examples.
Robert J Ray -The Weekend Novelist. NB First Edition Only.
This was the first creative writing book I bought, and it was an invaluable companion when I was writing my first novel. My copy is falling to pieces so I bought the second edition and - oh dear - he'd gone all academic and showing off his knowledge. I'm fairly experienced now as a creative writing book reader (let alone teacher and novelist), and I found it confusing and overcomplicated. Buy the first edition second hand if you have to.
Dibell, Scott Card and Turco - How to Write a Million.
Ignore the embarrassing title, this is actually three books in one, and two of the books - on Plot and on Character & Viewpoint - are excellent for craft techniques.