An excellent new volume is that by Robert C Kolb and Charles P Arand, The Genius of Luther's Theology (Baker Academic).  Not so much a study of Luther's thought as an interaction with him on the issues of righteousness and the word preached.  It's a robust, refreshing, stimulating, and challenging book for those interested in seeing how Luther's thought can yet inform modern church life.  Those wanting girlyman soulpatch metrotheology should look elsewhere.