Following the two great questions about programming books: The Definitive C++ Book Guide and List and The Definitive C Book Guide and List I'd like to propose creating such list for Assembly Language.
This might be an old and not so popular language nowadays, but I believe that good knowledge of it can only help in software development using higher level languages.
Please provide quality books and an approximate skill level. Because each processor have some number of their own specific instructions please no reference manuals - if someone will need one then it is easy to find it.