Newly or recently purchased
Justinian, The Digest of Roman Law
Justinian, The Institutes of Justinian
William of Ockham, A Short Discourse on Tyrannical Government (Cambridge Texts in the History of Political Thought)
John of Salisbury, Policraticus (Cambridge Texts in the History of Political Thought)
J.H. Burns, ed., The Cambridge History of Medieval Political Thought c.350-c.1450 (I had really thought that I already owned this, and now wish that I'd bought it on sale at APSA!)
Conciliarism and Papalism (Cambridge Texts in the History of Political Thought)
Gratian, The Treatise on Laws (Decretum Dd. 1-20 With the Ordinary Gloss)
Marsilius of Padua, The Defender of the Peace Cambridge Texts in the History of Political Thought)
Syllabus-building time is expensive! But at least this year I can usefully combine my book purchases for the undergrad class (Medieval and Renaissance) and the grad class (Foundations of European Studies).