In the past we read much of Bob Harper's "Practical Foundations for Programming Languages", 2nd Edition (http://www.cs.cmu.edu/~rwh/pfpl/2nded.pdf), with some excursions into other topics, including modal type theory and linear types, as well as implementations in Twelf and Idris. Our resident expert is Rowan Davies (http://www.cs.cmu.edu/~rowan/).
Some videos of past sessions are available via the following link, including two catch up sessions (highly recommended for new members):