The German slang word "gummi", which means "condom".
Many references to history and philosophy ("You, Kant, Always Get What you Want," and the deleted scene with Yitzhak's drag character, Krystall Nacht, as just two examples), and little German references in the lyrics ("sweet home Uber Alles!").
Manly Gay / Straight Gay / Camp Gay : Hedwig's back story is that she was a gay man who had the sex change operation to escape from Communist East Germany, not really a transwoman, so she tends to have a different interpretation depending on the actor. She is also usually played by men, with the sole exception of Ally Sheedy.
Tear Jerker: Almost every time a song involving Tommy and Hedwig in the same scene is going to be pretty emotional.