John Maynard Keynes, The General Theory of Employment, Interest and Money

 Prometheus Books, ISBN# 1573921394; Reprint edition (May 1997), $16.98 ($10.59 on Amazon);

 free online version at http://www.newschool.edu/nssr/het/texts/keynes/gtcont.htm)

 

 Thomas Malthus, An Essay on the Principle of Population

 Penguin USA (Paper), ISBN# 014043206X (June 1983), $18.00 ($12.00 on Amazon);

 free online versions at http://www.gutenberg.org/ebooks/4239 and

 http://www.econlib.org/library/Malthus/malPlong.html)

 

 Karl Marx, Capital, A Critique of Political Economy, Vol. 1

 Penguin USA (Paper), ISBN# 0140445684; Reprint edition (May 1992), $20.00 ($13.60 at Amazon);

 free online version at http://www.marxists.org/archive/marx/works/1867-c1/)

 

 David Ricardo, The Principles of Political Economy and Taxation

 Dover Pubns, ISBN# 0486434613 (June 2004), $10.95 ($8.37 at Amazon);

 free online versions at http://www.gutenberg.org/ebooks/33310 and

 http://www.econlib.org/library/Ricardo/ricP.html)

 

 Joseph Schumpeter, Capitalism, Socialism, and Democracy

 Harper Perennial ISBN# 0061330086 (December 1962), $16.00 ($10.87 or cheaper at Amazon);

 not out of copyright)

 

 Adam Smith, An Inquiry into the Nature and Causes of the Wealth of Nations

 University of Chicago Press (Trd), ISBN: 0226763749 (February 1977), $36.00 ($26.28 at Amazon);

 free online versions at http://www.gutenberg.org/ebooks/3300 and

 http://www.econlib.org/library/Smith/smWN.html)

 

 Frederick Winslow Taylor, The Principles of Scientific Management

 Dover Pubns, ISBN# 0486299880 (January 1998), $5.95 (same price at Amazon);

 free online version at http://www.gutenberg.org/ebooks/6435)

 

 Thorstein Veblen, The Theory of the Leisure Class

 Dover Pubns, ISBN# 0486280624; Reprint edition (May 1994), $3.50 (same price at Amazon);

 free online version at http://www.gutenberg.org/ebooks/833)