All Scheme challenged programmers (ahem, like me) should get:
On Lisp: Advanced Techniques for Common Lisp
by Paul Graham
Prentice Hall 1994
It covers all the cool advanced things you can do with Lisp, and about
half the book is dedicated to macros. It even has chapters on compilers,
atns, nondeterminism, OO (writing your own clos), and the poorly
documented (IMO) call-with-current-continuation.
Don't let the title deceive you, it has a good mix of Scheme and Clisp
examples.
Miguel, perhaps you can put a reference to this book on the gnome page.
Aldy