One of our C.V. Starr fellows and I were having an email exchange today about resources for students in our first year transnational practice course. One of the resources I cited to him was Larry Solum's Legal Theory Lexicon.
I assign posts from it every year to students - for example, I want my Civ Pro students to start with a somewhat more theoretical overview of procedural justice than our textbook provides, and I find Larry's post on Procedural Justice helps set up a good class discussion. As we labor through what constitutes the holding of a case and how holdings matter, I assign his post on holdings.
In general, I've found his posts to be accessible to first year law students, but also sophisticated and reliable. I also turn to them myself as a first resource when, as has happened a lot since I got to the academy, I find myself dealing with concepts long forgotten or never quite learned.
There must be other resources similarly deep and similarly reliable out there. I'm hoping that in the comments people will weigh in with free resources that are worth assigning to or at least sharing with students.