For starters:
The AssociationOfLispUsers maintains a list of lisp books at http://www.lisp.org/table/books.htm.
Not a CommonLisp book, but a must read, is StructureAndInterpretationOfComputerPrograms.
The Little Lisper, by Friedman and Felleisen, is an interesting Lisp book that could be considered a proto-patterns book. It's structured as a series of many small problem/solution pairs, each based in the context of earlier knowledge described in the book. Each chapter introduces an important programming principles and then explains it in terms of problem/solution pairs. -- NatPryce
[The most recent edition is now called TheLittleSchemer.]
OnLisp is a fine book, but I read through it just once and then fired off an error report to its author. ParadigmsOfArtificialIntelligenceProgramming I keep coming back to; it's practically a comfort book to me. It deserves attention outside the Lisp world. -- DariusBacon