Everyone seems to be getting in on the idea, so here is my own list.
Architecture: City Sense, Theo Crosby
It isn't too much of an exaggeration to say that this one book literally changed my life. I spent most of my time at school planning to be a chemical engineer. Once I knew that wasn't going to be, I was at a total loss. By chance I found this book in the local library, probably in 1965, the year it was published. One of the references was by Jane Jacobs (below) and from there I got into planning (and photography). I haven't read it or even seen it since then, but without it I wouldn't be typing this list.
Death and Life of Great American Cities, Jane Jacobs
I followed this up from a reference in Crosby's book. I was still at school then, (1965) but even now I can remember how it opened me up to all sorts of ideas. Published in 1961, it is still a brilliant dissection of why cities work, focussing on what really happens in peoples lives, not abstract politcial theory. Even after 45 years it should still be required reading for every planner, every would-be politician and anyone who wants to understand why things are not as they should be - which means all of us.
Uses of Literacy, Richard Hoggart
Another eyeopener for me. This book (written in 1957) I suppose opened up the possibilities. When I went in 1966, I think only about 4% of the population went to University. From my background it would have been even smaller. Hoggart's book, written around his own childhood in the north as a 'scholarship' boy resonated strongly for me and how I felt about myself and my class and effectively said 'you don't have to accept what others feel is appropriate for you - you can make your own opportunities'
A Guide to the Philosphy of Morals and Politics, C E M Joad
This book, in a wartime edition, was in the Sixth Form Library at my Grammar School. I can't claim to have read it then, but I did browse through it and was excited by the ideas it ranged over. I finally bought my own copy about 10 years ago. It is this book I credit with planting in me the idea of 'philosophical thinking' which seems to have surfaced at regular intervals over the years.
Unknown
It may seem bizarre to credit a book whose title I can't remember, but again whilst at school, I came on a book about Jazz. I had heard the odd bit of Chris Barber, but this book, which may have been Hear me Talkin to Ya by Nat Hentoff, brought out the real thing, as I remember it setting it in the context of being Black in 50s and 60s America and in the process introducing me to yet another life long passion.
New Maps of Hell, Kingsley Amis
By the time I read this I was already a fan of Science Fiction. I don't remember when I started reading it, but I recall books about Kemlo, the Space Boy (by E C Eliot) and other books by Capt W E Johns of Biggles fame. By the time I went to Grammar School, I was lucky in that my English teacher, while not a fan himself didn't automatically dismiss it as rubbish (Thank you Bill Wilson!) Through him I was introduced to the likes of Theodore Sturgeon (and Roald Dahl). In the library next door to the school, I found Clifford Simak, James Blish, Brian Aldiss (successfully managing to convince my mother that A Hand Reared Boy and A Soldier Erect were indeed SF!), Arthur C Clark (and Tolkien and Leslie Charteris and...). Amis' book however made me realise that SF wasn't just a minority interest, but something of merit in its own right.
I'm up to six books and haven't got out of the sixth form yet!
The Sociological Imagination, C Wright Mills
In the 1960s the venom now directed at Media Studies in Universities was focussed on Sociology. This book was for me a counterbalance to that and gave me an early introduction to the social sciences as a field of study.
Advertisements for Myself, Norman Mailer
I think this book was, for good or ill, my first exposure to the idea of writing as a craft, something that you worked at. I'm not sure if it was ever of any practical use in my own writing, but it remains entertaining and a great insight into Mailer's mind. Some of the essays are brilliant evocations of their period, although I suspect Mailer had more grandiose objectives for them. I still haven't read The Naked and the Deadthough!
Limits to Growth, Club of Rome
Something which will no doubt produce howls of derision from the likes of Philip Stott, but this book, like Crosby and Jacobs, was a watershed in my thinking about the world. Although its pessimistic findings have not held up, without it we would not be facing up to the environmental threats ahead, even in the half baked manner we have adopted so far.
The Complete Poems, Thomas Hardy
I've included this not just because I think Hardy is one of the greatest poets of the English language (and I do) but because it was this book which brought me back to reading poetry and even to thinking about writing it. (Don't worry, I won't inflict any on you - I'm no Vogon) From this I began to read poetry voraciously and began to understand what was going on behind the words.
A Pattern Language, C Alexander et al.
I'm cheating here, because this is number 11, but hey - its my list! No one with an interest in urban design or environmental issues should miss this. Like Jane Jacobs this is an outstanding description of what works, and as importantly how to make it work again and again.