Menachem Elon's four-volume Jewish Law: History, Sources, Principles (Jewish Publication Society) provides a good overview of Jewish law. Other useful treatises include An Introduction to the History and Sources of Jewish Law (Oxford University Press) and Jewish Law and Legal Theory (New York University Press).
The "Jewish Law" section of Religious Legal Systems: A Brief Guide to Research and Its Role in Comparative Law by Marylin Johnson Raisch discusses the basic sources of Jewish law and links to online resources. See also, David Hollander's "Jewish Law for the Law Librarian," 98(2) Law Library Journal 219 (Spring 2006).