Food

Schweinshaxe and anything with spargel in

Was there last weekend, only got time to check few places:

The Bird
http://www.thebirdinberlin.com/
Great american hamburger (recommended here too: https://goo.gl/yi95GS)

Hermanas wine bar
Warschauer Str. 81A

You can find good recommendations on the book above, I usually check it when travelling, it doesn't just list starred restaurants, but anything from a street stall or dirtiest restaurant to the most starred one, it's just where food is good.

munich

Go to Jagdschlössl at U Rotkreuzplatz for proper bavarian food.
http://www.jagdschloessl-muenchen.de
Definately recommend their "Münchner Tellerfleisch" and "Ofenfrischer Braten von der Sau"

dusseldof

..avoid "Alt" beer!

berlin

..like somebody said, there's a lot of great food in Berlin. There's also a lot of shit food in Berlin though.
Would help to know where you are and what you're after.
There are traditional / regional dishes in Berlin as well, but compared to bavaria it's basically all shit.