There’s a big museum at Arromanches; from memory there may also be something at Port-en_Bessin, overlooking Omaha Beach, but it was a long time ago (my visit, not the invasion, we all know when that was)
Bayeux also is not very far away, worth visiting to see the “tapestry”. US Paras also landed in Sainte-Mere-Eglise near Utah beach on the Cherbourg penninsula, but I don’t know if there’s anything particular there to commemorate(sp) it.
And of course Caen is also worth a visit. Most of it was flattened during the battle for the city but IIRC the original castle is still there, where William Duke of Normandy (and later William I of England) came from