Matilda of Flanders

You can't go wrong with Tracy Borman's Matilda: Wife of the Conqueror, First Queen of England is an excellent biography published in 2012 - detailed and accessible.  It's the only good full-length work on her, and it is very well-researched and accessible.

For William the Conqueror there are many good biographies, but my favourite is William the Conqueror by David Bates.  He's a good historian and really gets under his skin.  A longer. more academic, biography was written by David Douglas William the Conqueror: The Norman Impact Upon England. Definitely more for a scholarly audience but if you want the most comprehensive book on the market then this is the one.

My favourite book for this episode though is William Aird's Robert Curthose: Duke of Normandy. Robert is an utterly fascinating character, one of my favourites in history, and this is a beautifully written biography.  For an analysis of the relationship between Matilda and her eldest (and possibly favourite) son, this is perfect. 

In terms of contemporary sources, the best chroniclers for her are Historia Ecclesiastica of Orderic Vitalis, Historia Regum Anglorum of William of Malmesbury and Gesta Guillelmi of William of Poitiers.