Daniel P. Friedman, Mitchell Wand, and Christopher T. Haynes. Essentials of Programming Languages. Second edition. MIT Press, 2001.
R. Kent Dybvig, The Scheme Programming Language, Third Edition, MIT Press, 2003.
Language to specify when running it: Essentials of Programming Languages
This report is the official reference for the Scheme language and will tell you all you could possibly want to know about the language, including all the details about valid identifiers, etc.
Read through the text of Daniel Friedman's talk entitled The Role of the Study of Programming Languages in the Education of a Programmer, given at UNAM in April 2001.
Read Paul Graham's article Beating the Averages, which describes the use of Lisp to implement what became Yahoo Store.