Here is a new book from Broadman & Holman by David Allen which argues that Luke is in fact the author of Hebrews. It is not out until June, but I am already looking forward to hearing what Allen has to say. (I saw the announcement originally on Polumeros, a blog devoted to all things Hebrews.)
What I think is most interesting is that B&H lists this book as part of the NAC Studies in Bible and Theology series. I have enjoyed the NAC series and highly recommend most it as a reflection of good Evangelical scholarship. A supplement series with the same attention to quality is much appreciated.