In reply to drunken monkey:
It's a really good city but you won't be avoiding the crowds of British stag parties by going there, they got there years ago.
Oranienburg strasse is good for a few bars, we found a good cocktail place that had a happy hour from 4pm to 4pm and was open until 6am if you hadn't died before then.
We stayed in nollendorfplatz, it was a really nice posh area and hotel but possibly not the best place for a stag do because it's the the gay centre of the city.