Okay, found the book. This is information taken from Panther Paws, 11th Edition: Travel Europe
, a book geared to US military members living in Europe, so they are primarily, but not only, of interest to Americans.
First, a website: the American Battle Monuments Commission website is www.abmc.gov
, from which you can get oodles of info.
Okay, now the list:
Bastogne - the Bastogne Historical Centre commemorates this WWII battle.
Battle of the Bulge - lots of individual sites between Echternacht , Luxembourg and Maastricht, NL.
December 1944 Historical Museum in La Gleize (Ardennes)
Malmedy - there was apparently a massacre in this town, which I've actually visited, unaware of it's historical significance. It's quite a lovely little place, very friendly people. And the last gas station for 70 kms.
Waterloo - I was just there, a couple of weeks ago. The more you know about the Napoleonic wars, the more you'll get from this otherwise anticlimatic spot, just a little ways outside Brussels.
Ypres - this was a major Canadian/British battlefield in WWI, might have more significance for them than for Americans, but apparently there's some great memorials/museums/monuments there.
Chateau-Thierry - near Reims, this is the area of the Battle of Belleau Wood (US, WWI)
Battle of the Somme - (British/Canadian, WWI) - they recommend Thiepval Memorial, Newfoundland Memorial and Beaumont Memorial Parks, and I personally recommend Vimy Ridge to any Canadian, or anyone who has read All Quiet on the Western Front
. Old ladies in the village of Vimy came out and greeted me when they saw the flag on my pack.
Verdun - lots of memorials and cemetaries in this area. Keep off the grass, there is unexploded ordinance. (Same goes for Vimy.)
Normandy beaches: Everyone raves about the military museums, memorials and monuments along the length of the beaches.
The castle at Clervaux has a small military museum. Only open May trhough September, though.
Diekirch: another pretty town with an ugly past. The National Museum of Military History gets high marks in this guidebook - "outstanding" and "well worth the visit", apparently.
Ettlebruck: General Patton Memorial Museum
Hamm American Cemetary: just outside Luxembourg City, this is the site of Patton's grave, as well as those of thousands of other soldiers. We went for Remembrance/Veteran's Day services last year, it was very moving. Some great maps depicting all the various battles, and apparently the staff there are knowledgeable (I believe they're all vets) and willing to answer lots of questions, as well as find any particular gravesite you might be looking for.
Oosterbeek: The Hartenstein Airborne Museum gets the nod.
Hope that helps a bit.