Library of Economics and Liberty

Econlib has a huge collection of online books on Economics, including some of the classics:

Adam Smith

Wealth of Nation by Adam Smith Principles of Economics by Alfred Marshall Capital: A critique of political economics by Karl Marx The Theory of Money and Credit by Ludwig von Mises

 [H]e intends only his own gain, and he is in this,
as in many other cases, led by an invisible hand to
promote an end which was no part of his intention.
 Nor is it always the worse for the society that it
was not part of it. By pursuing his own interest
he frequently promotes that of the society more
effectually than when he really intends to promote it.
 I have never known much good done by those who
affected to trade for the public good.

                    ---- Adam Smith, Wealth of Nation