My first date with my then future wife was at the Panorama museum of the battle of Stalingrad.
In France there is a very good armour museum in Saumur
http://www.musee-des-blindes.asso.fr/
If you go to Normandy be sure to visit Caen and the museum just outside of there - there is also a fantastic, small and friendly restaurant in the cathedral close where you will taste some of the best food you are ever going to have. They speak English but do appreciate it if you make the effport to speak French, no matter how badly. If you're taking the GF, a romantic candlelit dinner there in the shadow of a great gothic cathedral = win and you will get enough to karma points to carry you through several future arguments.
If your French is a bit better you could also visit the farm of M. Samson in the village of Cintheaux on the Falaise road. His grandad collected loads of odds and sods left over after Operation Totalise and put them in his barn. He has loads of great stuff, including several bits of a Tiger which was destroyed very close by. Not 100% sure but there is a good chance it was Wittmann's. It's at No 1 Rue du Prieure, Cintheaux. You will need good French though and it's always nice to take him a bottle of something for taking time out of his day to show you round. I can give you his contact details if you want to arrange a visit. Cintheaux has this weird kind of travelodge place outisdeit which is very cheap - it's also near enough to Caen to drive in for the grub (about 15 minutes).
Other places I know of worth a visit are Pilsen in Czech republic - it's not as commercial and geared towards Brit lager louts as Prague (also not quite as historical) but it WAS liberated by Patton and does have the best beer in the world - almost beyond dispute.
These are the only places I know well but there are plenty of others people will be able to share with you. Most importantly you're going to get a great taste of Europe and, for that purpose, any theme (WW2, food, etc.) is as good as the next.