We plan to visit Normandy and parts of France, Belgium, Netherlands. Would like maps and guide books that would cover important sites during the invasion and battles of WWII.
I haven't used it, but I know there is a book entitled "The 25 Essential WWII Sites, European Theater". You can find it on Amazon.
One plug for a museum that is a surprising treasure-trove of WWII (and WWI) artifacts that many military-minded tourists overlook: The Royal Museum of the Armed Forces and Military History in Brussels. They have a huge collection of exhibits that cover WWI, the interwar era, and WWII. Although the documentation is only in French and Dutch, most of the exhibits speak for themselves.
We use the battlefield guides by Major and Mrs. Holt. Here is alink to the available books at Amazon:
http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Dstripbooks&field-keywords=holt+guides+battlefields
They are great, as they are full of self guided tours. They will cover different battles, so you need to know your history and where you will be. They will start you at a specific point, say to set the odometer to zero, and give turn by turn instructions. Before each tour, there is an overview of the battle and what happened, who was involved, etc. I was able to locate Joyce Kilmer's grave and the site where he died this fall with their tour. Highly recommend these.
One site you may like concerns Henri Chappelle cemetery in Belgium.
If you go to the Battlebus website, they have a tab which lists recommended books on WW2.
http://www.battlebus.fr/Books.html
By the way, if you are going to Normandy, I HIGHLY recommend the battlebus tour rather than just visiting with a guidebook. I took the two-day American Experience tour recently and it was outstanding. I learned far more than I ever would have on my own. The guide was incredibly passionate and knowledgeable about WW2. I spoke to a couple in the hotel who had taken the Canadian tour and they felt the same way about their experience.