Several interesting books are available free online: Paul Graham's On Lisp describes many of the concepts that ended up in Arc. Practical Common Lisp is a very interesting guide to Lisp, Common Lisp the Language is a good reference, and Structure and Interpretation of Computer Programs is perhaps the best way to learn Scheme.
Useful print books include Paul Graham's ANSI Common Lisp, the print editions of Practical Common Lisp and Structure and Interpretation of Computer Programs, The Little Schemer, and Peter Norvig's Paradigms of Artificial Intelligence Programming.
Copyright 2008 Ken Shirriff.