The Technik Museum in Speyer
The Speyer museum has plenty of attractions for the WWII crowd - check out just a few of the exhibits here and more at their website
OK,OK,  it's a post-WWII sub, but it's darned interesting! This U9 was in service from 1967-1993.  You can climb inside and see the berths, periscope, control area, tiny officers' quarters, galley, torpedos, and lone toilet for 22 men. Then rent the movie classic "Das Boot" to get the full effect.
(L) A Messerschmidt Bf-109 from 1942, one of the most famous German fighter planes.
(Right) Note the Iron Cross still visible on the wing of a Messerschmidt 110 raised from a Norwegian lake. The whole display shows other parts of the 1942 aircraft excavated from the Kiruna See following an emergency landing in 1945.
                 "Wheels Must Roll For Victory!"
This propaganda placard written in highly colloquial style glorifies the wartime role of the German railroads.  Joseph Goebells used the slogan in a Feb 1943 speech, exhorting the German people to free the rails for war-related traffic. This gets my vote as the creepiest exhibit in the museum.  
Several Reichsbahn trains can be examined close-up, including the engineer's compartment
The "10 Important Rules" are written in a slangy style using the pronoun "du", common only with close friends