A little while I was going through a some what low ebb (not helped by the stress of bday outfits! ;)) however I searched through our own personal library, otherwise known as what was the spare room!, I found http://www.amazon.co.uk/Indestructible-Self-belief-Seven-Getting-Keeping/dp/0749924950 by Fiona Harrold and http://www.amazon.co.uk/Change-Your-Life-Seven-Days/dp/059305055X by Paul McKenna. Books I had bought a earlier times to read but had never got round to, and I wish I had! I read Fiona Harrold's in one day and then Paul McKenna's over the next seven consecutive days. They are both such great reads and I feel like they have actually changed my outlook.
Harrold's book focuses on self belief, of which confidence is a factor, full of encouragement, activities to change your beliefs and very inspiring stories! McKenna's is much broader and more about changing your life as a whole however that of course adds to confidence! So two very recommended reads there! :)