A Brief History of Programming Languages
   A special Byte Magazine article published for Byte's 20th anniversary special report
   http://www.byte.com/art/9509/sec7/art19.htm

Computer Languages History
   Timeline chart, 1954 to today, printable; links to homes of many languages.
   http://www.levenez.com/lang/

Diagram of Languages
   Two diagrams showing how many languages are related to each other.
   http://merd.sourceforge.net/pixel/language-study/diagram.html

Historic Documents in Computer Science
   Original, historic first documents for many early programming languages, like language manualsa, scanned and converted to PDF form.
   http://www.fh-jena.de/~kleine/history/

History and Comparison of Programming Languages
   Papers on use history of: comments, labels, literals, parentheses.
   http://www.gavilan.edu/csis/languages/history.html

History and Evolution
   A list of computer languages and some links to compilers for these languages.
   http://www.scriptol.org/history.php

O'Reilly: The History of Programming Languages
   A poster plots over 50 programming languages on a multi-layered, color-coded timeline.
   http://oreilly.com/news/languageposter_0504.html

The History of Computer Programming Languages
   Short concise article on programming language history with some links.
   http://www.princeton.edu/~ferguson/adw/programming_languages.shtml

The Semicolon Wars
   History and critique of disagreements over language design details, citing some specific traits; by Brian Hayes. American Scientist.
   http://www.americanscientist.org/template/AssetDetail/assetid/51982/

Visual Programming Languages: A Survey
   This paper by Marat Boshernitsan includes an historical overview of some of the pioneering efforts in the field.
   http://nitsan.org/~maratb/cs263/

Wikipedia: PL/I
   An encyclopedia description of PL/I history with many links to programming terms.
   http://en.wikipedia.org/wiki/PL/I_programming_language