http://tuvalu.santafe.edu/~wbarthur/Papers/All%20Systems%20G...
He has a new book with all his papers: Complexity and the Economy (http://www.amazon.com/Complexity-Economy-W-Brian-Arthur/dp/0...). I have not bought it yet. The preface is free to download here: http://tuvalu.santafe.edu/~wbarthur/Papers/Complexity%20&%20...