I’m no big fan of Döner (turkish kebap), to be honest. But rumor has it, that this by now favorite German dish …
… was invented in Berlin. And you do get a good one in the city. So it can’t be left out here.
I think Bagdad has a fairly good one, with good meat and the choice of chicken or beef. I prefer beef.

Bagdad, Schlesisches Tor, thanks for the pic to http://berlin.virtualnights.com
It is in Schlesische Straße, just off the subway stop Schlesisches Tor.
There is another Döner restaurant right next to it, don’t go there. I don’t like it out of no reason. (But I have friends who enjoy their Döner there as well - so this is just a very personal statement).
My favorite is a Dürüm Döner with extra cheese and olives (Eur 3,40), but the standard Döner (”Ein Döner bitte”) for 2,50 is great, too. Concerning sauces on the döner, they salesperson will ask you “welche sauce”, I prefer “Kräuter-scharf” meaning a mix of the spicy and herbal sauces. There is a garlicy one as well. Concerning condiments he will ask you “Mit Salat alles” which means you get lettuce on it, tomatoes, onions and cabbage.
The mentioned rumor has it that the Döner was created or developed in Berlin in the 60s (in Turkey, there is a beef-in-bread-kombo, but it doesn’t have any condiments on it). Who knows whether this is true, but if it is true, the Döner’s origins lay in a Turkish restaurant in Adalbertstraße: it is on the left hand side when you turn in from Oranienstraße and walk towards Kottbusser Tor. They still sell Döner, also to go, and it is - in fact - very good.