Since I started blogging about philosophy of economics, I regularly get asked by graduate students in philosophy for reading suggestions in economics to acquaint them with the field. While the responsible answer is that economics has become too vast even for seasoned practitioners (and I am at best a part-time philosopher of economics and I tend to rely on informants in the discipline), I do try offer sincere responses tailored to my correspondents' philosophic interests. Having said that, if one wants to understand mainstream economics (and even its evolution during the last half-century) from within, one should just start reading Paul Samuelson's collected scientific (!) papers--he defined the field from the mid 1940s onward. (If one reads his footnotes and the folk that responded to him, one grasps what happened in the field.)
However, as I have hinted before if one wants to understand the world we live in -- that is mixed economies in which vast state bureaucracies try to maintain ersatz-markets in various ways -- then the now largely forgotten Oskar Lange is a good place to start (with excursions to Eucken, Minsky, and Elinor Ostrom for developing one's thinking). What do readers think?