Just some links to other works inspired by Fritz Haarmann.
Kiełbasy Harmanna (Polish for Haarmann's Sausages, although the killer's surname is a little misspelled): a song by Polish rock group T-Love. Listen here (hat tip to Maciej K. and Maciej Z. for this link).
The Oi group Rabauken published a CD entitled Warte, warte nur ein Weilchen... in 1993. With the picture of Fritz Haarmann being conducted to the prison on the cover and an Oi version of the well known song.
The American extreme metal group Macabre went even further by recording two songs about the "Werewolf from Hannover": Fritz Haarman The Butcher in 1989 and Fritz Haarmann der Metzger in 2003 (this is not a German version of the previous song, but rather yet another paraphrase of the already classic Warte, warte...).
And last not least, Wumpscut's leader Rudolf "Rudy" Ratzinger (also founder of Beton Kopf Media) seems obsessed with Fritz Haarmann and other cannibal stories. In fact the label's logo uses a picture of Haarmann:
And obviously Wumscut quotes the famous lines in one of its songs: Warte, warte nur ein Weilchen...
Guido Zurli's movie The Mad Butcher (1970) starring Victor Buono has sometimes been described as inspired by the story of Fritz Haarmann, but its plot is rather an amalgam of mythicized biographies of Carl Grossmann and Adolph Luetgert with many other aditions.
Mikita Brottman's Meat Is Murder: An Illustrated Guide To Cannibal Culture is an excellent read if someone is interested in more cannibal related movies.