T A is quite right - Pallud's monumental book is a classic work about the 'Bulge'. Two health warnings, though - it's very heavy and will crush your chest if you try to read it in bed, and the 'then & now' format is so tantalising that you will not rest until you have walked the battlefield !
Another one worth considering is Michael Reynolds'
'The Devil's Adjutant' ( Spellmount, 1995 ) which, despite the misleading title, is really a step-by-step account of the march of Kampfgruppe Peiper with many personal accounts from both sides. Obviously, this book concentrates on only one aspect of the Ardennes fighting, but gives a very good 'feel' for many of the grimmer aspects .