Most of the sex shops are to be found in the area around the central station (Hauptbahnhof), i.e. the Landwehrstraße and Schillerstraße area.
Beate Uhse is a well known Germany-wide chain of sex shops with 4 or 5 branches in Munich - one on Neuhauser Straße between Marienplatz and Karlsplatz, the other on Barerstraße near the central station.
See also: