I got asked about Berlin by a mate a few years ago.. I got this info from a friend who has lived there for a number of years..
Mitte: A lot of nice Bars are on Weinbergweg/Kastanienalle/Linienstraße/Torstraße (I like "Odessa Bar" Torstraße 89, Ecke Gormann, "Bar 3" on Weydingerstr. 20 or "august II." on auguststrasse 2
Kreuzberg und Neukölln: "little otik" is a tiny restaurant in Kreuzberg, Graefestr. 71 where they normally serve simple but good food, in the neigbourhood you'll find some nice bars as well ("Zum Fuchsbau" on Planufer 95 f.e.), some Bars/Clubs on Skalitzer Straße you might like as well ("Farbfernseher", "Monarch", "Westgermany" or "Möbelolfe"). Or in some distance "Ritter Butzke" (Ritterstraße 26, a today mostly by the young easyjet-set partypeople joined electro club)
Around metro station "Schlesisches Tor" are some nice places as well: for example the small electro club Chalet (Vor dem Schlesischen Tor 3)
A mixture between immigrant neighborhood and international Hipster Community define the northern parts of Neukölln; especially around Weserstraße you find some nice spots in an interesting surrounding (I would recommend "Das Tier")
Neue Odessa Bar - I have had some mad nights in there.
And judging by all your friends comments I’m sure our paths will have crossed as all those places are regular spots when I’m on a big night out. I’m not keen on Das Tier these days though. The staff are quite wanky at times and it’s not as fun as it once was.