If you're still there... The Technikmuseum is cool, and if you fancy a banging club night out, K17 is awesome. Although I've just read that it's closed, so that's out. There's is/was a great bar called Access, just off Alexanderplatz. They don't seem to have a website so I'm not sure about that. Charlie's Beach, behind the Berlin Wall is a lot of fun. And the Tiergarten is worth a wander around.
It's been a while since I've been. Last time I went was with my bandmate, Andy, and our whole thing was to be as deliberately offensive as possible. He stuck to this more rigidly than I did, and so had a bunch of SS symbols and swastikas all over his jacket. Which he was wearing when we met to go to the airport.
"Dude, you really can't wear that."
"Why?"
"It's illegal. You'll be instantly arrested."