Bird by Bird by Anne Lamott is a wonderful, easy-to-read and entertaining book on writing. Full of great life advice, too.
On Writing by Stephen King has practical tips -- such as axing those pesky adverbs -- and also discusses the writing techniques that work best for him.
How to Write a Damn Good Novel by James Frey: Terrible title, but if you can get past that it has very good tips on conflict and 'raising the stakes'.
Any other favourites out there?