This a league table of the most popular books that have been (or are going to be) read by UX book clubs based on information available through this site. It isn't comprehensive, but it's interesting nonetheless.

	Sketching User Experiences (UK, CA, DE, FR)	Bill Buxton	Sydney, Melbourne, London, Israel, Atlanta, Dallas, Denver Colorado, New York, Philadelphia, Toronto, Twin Cities, Washington DC, Helsinki, Edmonton, Zuid-Holland
	Don't Make Me Think (UK, CA, DE, FR)	Steve Krug	Canberra, Memphis, Los_Angeles, Boston, Milwaukee, Edmonton, Bristol, Wroclaw, Belfast, Hamburg, Glasgow
	Mental Models (UK, CA, DE, FR)	Indi Young	Boston, Brisbane, Canberra, New York, Portland, Auckland, Denver Colorado, Brighton, Zuid-Holland, Rome
	Designing for the Social Web	Joshua Porter	Sydney, Chicago, Denver, Colorado, Glasgow, Edmonton, Brattleboro, St Albans, Warsaw, Wroclaw
	Subject to Change (UK, CA, DE, FR)	Peter Merholz et al	New York, Richmond VA, Boston, Sydney, Toronto, Portland, Copenhagen
	Web Form Design: Filling in the Blanks (UK, Rosenfeld)	Luke Wroblewski	Ithaca, Warsaw, Toronto, Atlanta, Wroclaw, Sydney
	The Design Of Everyday Things	Don Norman	Edmonton, Bristol, Portland, Wellington, Vancouver, Glasgow
	A Project Guide to UX Design	Russ Unger & Carolyn Chandler	Chicago, Philadelphia, Toronto, Edmonton
	The Back of the Napkin	Dan Roam	Silicon Valley, Portland, Melbourne, San Francisco
	Emotional Design	Don Norman	Brisbane, Toronto, Auckland
	Communicating Design	Dan Brown	Bristol, Denver Colorado, Rome
	Design Is the Problem	Nathan Shedroff	Washington DC, Auckland, Switzerland
	Designing Interactions	Bill Moggridge	Atlanta, Calgary, Glasgow
	The Creative Habit	Twyla Tharp	Chicago, Dallas
	Glut: Mastering Information Through the Ages	Alex Wright	Canberra, Sydney
	Designing for Interaction	Dan Saffer	Austin, Melbourne
	Designing Gestural Interfaces	Dan Saffer	London, Los Angeles
	Designing for the Digital Age: How to Create Human-Centered Products and Services	Kim Goodwin and Alan Cooper	Seattle, Melbourne
	Nudge	Richard H. Thaler	Los Angeles, New York
	Measuring the User Experience	Thomas Tullis and William Albert	Washington DC, Warsaw
	101 Things I Learned In Architecture School	Matthew Frederick	Melbourne, Canberra
	The Humane Interface	Jef Raskin	Cologne
	The Myths of Innovation	Scott Berkun	San Francisco
	Designing the Obvious	Robert Hoekman Jr.	Twin Cities
	About Face	Alan Cooper et al	Los_Angeles
	Neuro Web Design	Susan Weinschenk	Dallas
	Web Design for ROI	Lance Loveday	Warsaw
	Understanding Comics	Scott McCloud	London
	The Design of Future Things	Don Norman	Canberra
	The 7 Habits of Highly Effective People	Stephen R Covey	Canberra
	Card Sorting: Designing Usable Categories	Donna Spencer	Brisbane
	Elements of User Experience	Jesse James Garrett	Groningen
	The Art of the Interview: Lessons from a Master of the Craft	Lawrence Grobel	Canberra
	The Social Life of Information	John Seely Brown	Cleveland
	Ambient Findability	Peter Morville	Brighton
	Small Pieces Loosely Joined	David Weinburger	Canberra
	The Essential Difference	Simon Baron Cohen	Canberra
	Designing Web Navigation	James Kalbach	Warsaw
	The Paradox of Choice: Why More is Less	Barry Schwartz	Brighton
	Tribes	Seth Godin	Twin Cities
	Getting Things Done	David Allen	Brattleboro
	Wired to Care	Dev Patnaik	Edmonton
	Re-imagine	Tom Peters	Canberra
	Thoughts on Interaction Design	Jon Kolko	Sydney
	In Pursuit of Elegance: Why the Best Ideas Have Something Missing	Matthew E May	Brisbane
	Landing Page Optimization	Tim Ash	Warsaw