Berlin Wall
A large stretch of intact Wall can be found to the east of the city centre along the River Spree in Mühlenstraße near the Oberbaumbrücke.
Known as the East Side Gallery, it is a section of the wall that is preserved as a gallery.
This can be easily reached from Ostbanhof or Warschauer Strasse. It has many beautiful murals, politically motivated and otherwise.
Another place to try is near the Martin Gropius Bau museum, currently under reconstruction. Two small pices are also in Potsamer Plaz and in its neighbourhood at the corner between Eberrtstraße and Bellevuestraße.