Nutella is a pathological example. It's a running gag among German speakers that they cannot figure out its gender. The discussion usually ends when someone suggests something like "das Nutellaglas" ("the jar of Nutella"), i.e. building a compound word so that the other part of the word imposes its gender.

EDIT: This may be interesting for you though. https://en.wiktionary.org/wiki/Appendix:German_nouns_which_h...