aye, get over to Friedrichshain-Kreuzberg.
Lots of great clubs and cafes/bars. Perhaps U-bahn to Frankenfurter Tor and move down through F-Hain towards Warschauer Str. (East-side gallery nearby), over lovely bridge to Kreuzberg and Gorlitzer
Try to find the old GDR industrial estate (you'll either wander into it, or miss it - down some steps before Warschauer U-Bahn crossing from the East) :D
Neukoln and Wedding are worth checking out - a bit rough round the edges, but getting more interesting. Prenzlauer-Berg (Mauerpark) is worth a visit
Gonna be fuckin freezin in Jan - take some wooly undergarments, lol.