Schimpfwörterbuch- Extensive list of German insults in an old book from 1839.
Schimpfwortliste - Very extensive list of German insults (licensing-statement at that page shows that words may be used at Wiktionary under GNU-FDL and CC-BY-SA 3.0 Unported).
InsultWiki - Wiki-based collection of German and English insults (licensed under CC-0).