Conrad Barski - Land of Lisp: a fun introduction to Lisp for beginners, with a game-like approach and lots of great illustrations.

Peter Seibel - Practical Common Lisp: Peter Seibel is one of the big names in computer science and a passionate advocate of Lisp and functional programming, this book is perfect as a reference manual for specific topics but you can read it front to finish as well to get a good Lisp introduction.

David S. Touretzky - Common Lisp: A Gentle Introduction to Symbolic Computation: another book for Common Lisp beginners, not as fun as the Land of Lisp but free of charge.

Paul Graham - On Lisp: a book for intermediate/advanced Lisp programmers, that gives the reader a better feeling of the language. Best book for those who want to become expert in the Lisp macro magic.