Introduction to Economic Analysis, by R. Preston McAfee (2007). ‘Open source’ intermediate undergraduate microeconomics textbook. Website also has slides for teaching.

Introduction to Modern Economic Growth, by Daron Acemoglu (2007, draft). Advanced economic growth theory.

The Econometrics of Macroeconomic Growth, by Steven Durlauf, Paul Johnson and Jonathan Temple (2004, draft). Advanced growth textbook.

Environment Economics, by Ross McKitrick (2007, draft). Intermediate environmental economics textbook.

Against Intellectual Monopoly, by Michele Boldrin and David Levine (2007). A critical analysis of intellectual property.

Invisible Engines, by David Evans, Andrei Hagui and Richard Schmalensee (2007). Non-technical book about two-sided software platforms.

Lecture notes in Microeconomic Theory, by Ariel Rubinstein (2006). Advanced microeconomic theory textbook.

Discrete Choice Methods with Simulation, by Kenneth Train (2003). Advanced textbook on estimating and simulating discrete choice models.

Industrial Organization: A Strategic Approach, by Jeffrey Church and Roger Ware (2000). Intermediate industrial organization textbook.

Short Course on Nonlinear Pricing, by Robert Wilson (1999). Advanced textbook on nonlinear pricing theory and applications.

Law’s Order: An Economic Account, by David Friedman (1999). Economics of the law.

Modelling Bounded Rationality, by Ariel Rubinstein (1998). Game theoretic models of bounded rationality (advanced).

Economics and Language, by Ariel Rubinstein (1996). The economics of language and language of economics.

Price Theory, by David Friedman (1990). Intermediate microeconomics textbook with a slightly unconventional viewpoint.

Bargaining and Markets, by Martin J. Osborne and Ariel Rubinstein (1990). Advanced bargaining theory textbook.

There is also the Library of Economics and Liberty, which has many digital copies of historical economics texts available for download.