Wex, according to Wex, is "an ambitious effort to construct a collaboratively-created, public-access law dictionary and encyclopedia. It is sponsored and hosted by the Legal Information Institute at the Cornell Law School (http://www.lawschool.cornell.edu/). Much of the material that appears in Wex was originally developed for the LII's "Law about..." pages, to which Wex is the successor."
Wex has a clean and attractive interface, and each article includes, on the right side of the page, a nicely ordered "menu of sources" for further reading. (See for example the menu accompanying the death penalty article).