NOTE: This page was created for my Philosophy of Economics, Philosophy of Social Science, and Intro to Philosophy courses at the University of Pennsylvania.
In general, while Wikipedia is great, Britannica Online has the advantages of being reviewed by academics and having some fancy features. But you need to consult it on campus, since it's for subscribers. Below you'll find more domain-specific resources.
Here are some handy online encyclopedia (like if you want to know how philosophers define "empiricism"):
If you want to know what philosophy of science is: Philosophy of science entry in Britannica (subscription: consult on campus). Here are some other nice entries: Scientific realism and antirealism in REP.
For entire books etc. check The Internet Archive: All of the philosophy classics are available here. The Internet Archive is an online library with historical collections (text, audio, movie) in digital format - all legal, since they only publish things for which copy rights have expired or have been wavered. Fantastic.
Not everybody in class will have the same background. For those who want an introduction to econ, there is plenty of free stuff online.
Reference work: New Palgrave Dictionary of Economics (subscription: consult on campus)
Some nice (top) journals with understandable summaries of today's research:
Some encyclopedia entries on philosophy of economics:
Philosophy of economics journals: