really bizarre is the cyankali bar
http://www.zyankali.de/
also wacky was a bar next to the entrance of the "hackesche höfe", you see a red light strip in the air..follow that! I forgot the name. Anopther one is the "lee harvey oswald" bar next to Boxhagener platz...I am not sure if its still there...
a fantastic little place is the bebop bar, willibald alexis strasse, "insider kreuzberg", with great jazz jamsession on sunday, and maybe even better, the "Arcanoa" (also X-Berg) or even ACUD in mitte (near Rosenthaler Platz) for colourful people and music.
illegal: try to get into a meeting of Mastul, a "cultural society" in Wedding
http://www.mastul.de/start.html
also illegal, there used to be "Kino durch's fenster" (cinema through the window) in Friedrichshain, where you had to enter the cinema room (aka living room) through a window.
Nice food: go to "Lei und Lui" in the wilsnacker strasse...somewhere between italy/middle east/.... wild combinations but fantastic and cheap.
buy yourself a "Zitty" magazine and check out what's going on!