Condition Handling in Common Lisp
The condition handling system in Common Lisp has a very rich feature set compared to the error handling features in commonly used languages today. Kent Pitman wrote a paper entitled "Condition Handling in Common Lisp" for a book, published in 2001, about advances in exception handling techniques. It's a great overview of the history of error handling techniques in programming languages as well as a great overview of how Lisp handles the issue.