The D Day landing beaches were a must see for me when I visited France. Something I would recommend anyone with even a remote interest in WW2 history. We were lucky enough to stumble upon a memorial service at the American cemetery at Colleville-sur-Mer and got to speak to an English paratrooper veteran. Very moving and humbling experience. For more information, have a look at this site http://www.history.com/topics/world-war-ii/d-day
I did a tour organised through these people http://normandy.memorial-caen.com/organise-your-visit. Do your self a favour and ask for Kendra. She was fantastic. There were some real history buffs on my tour and they were suitably impressed by her.