Several of these come to mind right away. The first is just south of Hoheluft brücke and is of gray cats laying on a windowsill. The second is near the Billstedt Einkaufzentrum on Schiffbeckerweg and it is an underwater scene. Another is on Muehlendamm in Hamburg on the left handside of the road if you are heading towards Berliner Tor right if you are headed towards Mundsburg.
There is an old Del Monte advertisement on a building on Amsinckstrasse past the ADAC by a lot near the Huhnerpost. Ive included this one because it isnt a standard framed billboard but a painted mural.
Im sure there are more through out the city but these are definitely worth checking out.
NOTE : THe buliding in the photo has unfortunately been repainted and the art covered.

