This is not meant to be a comprehensive book list – just some that I would recommend personally. They are also not all strictly about permaculture, but are all about related subjects.
Aranya’s Permaculture Design Step-By-Step Guide (£14.95 plus £2 postage) – Brand spanking new
Bill Mollisons Designers Manual (£70 inc. postage) Classic book
Permaculture: Principles and Pathways Beyond Sustainability by David Holmgren (£19.95 plus postage)
The Transition Handbook by Rob Hopkins (£11.95 plus postage)
Creating a Forest Garden by Martin Crawford (£30) I use this book a lot for choosing plant species.
Seaweed and Eat It by Xa Milne and Fiona Houston (RRP £10.99) I adore this book – It changed how I eat!
The Self Sufficientish Bible by Andy and Dave Hamilton (£30 plus postage)
One Straw Revolution by Masanobu Fukuoka (£9.50 plus postage)
Siddhartha by Hermann Hesse – This is not strictly a permaculture book, but I think everyone should read it.
Also “Radical Homemakers” by Shannon Hayes