You can read online or download the entire US Army Center of Military History’s official history “The Ardennes: Battle of the Bulge,” by Hugh M. Cole.
http://www.history.army.mil/html/books/007/7-8-1/index.html
S.L.A. Marshall’s “Bastogne, the First Eight Days” is online at:
http://www.history.army.mil/books/wwii/Bastogne/bast-fm.htm
I also recommend Charles MacDonald’s “A Time for Trumpets,” and John Eisenhower’s “The Bitter Woods.”
Janice Holt Giles’ “The Damned Engineers” is about the 291st Engineer Battalion (Combat) previously mentioned in this thread.
The Green Books!