Love Hamburg, but I think Reeperbahn is a bit too much. I prefer the Altona district, it got a nice feeling. Kind of Stockholms Söder mixed with Christiania. Altona used to be a danish city until 1864!
I've been to the FC St. Pauli fans pub a couple of times (Jolly Roger), it's quite shabby but the music can be good. That is if you like soul, ska, 2-tone, punk and so on. Speaking of FC St. Pauli, there is a new fictional movie released in March about their fans: http://www.gegengerade-derfilm.de/