Books

ANSI Common Lisp
By Paul Graham; Prentice Hall, 1995, ISBN 0133708756. Tutorial introduction of essential Lisp programming concepts, plus a convenient, up-to-date reference manual, for ANSI CL.
http://www.paulgraham.com/acl.html

Best Lisp Books
A variety of books on Common Lisp programming and AI, personally chosen by an experienced developer.
http://www.apl.jhu.edu/~hall/lisp-books.html

Common Lisp: A Gentle Introduction to Symbolic Computation
By David S. Touretzky; Benjamin-Cummings, 1989, ISBN 0805304924. Fine introduction for beginners; even one who never programmed before in any language will be able to use this book, yet covers all relevant topics thoroughly. Full version online, two formats.
http://www.cs.cmu.edu/~dst/LispBook/

Common Lisp: An Interactive Approach
By Stuart C. Shapiro; W.H. Freeman, 1992, ISBN 0716782189. For advanced CS students, undergraduate and graduate, stepped tutorial, many exercises and assignments for hands-on learning. treats functional before imperative programming, covers CLOS. Full version online, several formats.
http://www.cse.buffalo.edu/pub/WWW/faculty/shapiro/Commonlisp/

The Common Lisp Cookbook
Collaborative project; goal: write for CL a work similar to O'Reilly Media's Perl Cookbook.
http://cl-cookbook.sourceforge.net/

Lisp Books and Information
Guide to online Lisp resources.
http://www.lispmachine.net/

Object-Oriented Common Lisp
By Stephen Slade; Prentice Hall PTR, 1998, ISBN 0136059406. Likely the best book available on using a CL environment for uses other than AI programming.
http://www.pearsonhighered.com/educator/academic/product/0,3110,0136059406,00.html

On Lisp
By Paul Graham; Prentice Hall, 1993, ISBN 0130305529. Thorough study of advanced methods, with bottom-up programming as unifying theme. First full description of macros and their uses. Covers important topics related to bottom-up programming: functional programming, rapid prototyping, interactive development, embedded languages. Free download, PDF.
http://www.paulgraham.com/onlisp.html

Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp
By Peter Norvig; Morgan Kaufmann, 1992, ISBN 1558601910. Overview of classical AI programming, valuable history lessons, basic introduction to Lisp, efficiency considerations.
http://www.norvig.com/paip.html

Practical Common Lisp
By Peter Seibel; Apress, 2005, ISBN 1590592395. Focus: putting CL to practical use with example projects: spam filter, ID3 parser, Shoutcast server. Source code downloads. Full version online.
http://www.gigamonkeys.com/book/