Doberman Pinscher
Dobermans have often been used by the military, and often bred and trained to be aggressive, even being bred for dog fights at one time. There are a number of horror stories from the 1970s, when Dobermans became quite popular, about them attacking their owners for no apparent reason, except seeing them act aggressively towards strangers or intruders. Despite these occurrences becoming much more infrequent since then, insurance companies are often wary of this breed, and may spike your premium significantly.
German Shepherd
German Shepherds are thought to generally make great pets are they are obedient, intelligent, and loyal dogs, reasons they are often used in law enforcement. However, it is this intelligence which also makes them quite independent and strong-willed, so without the right training, they can be hard to handle. It is also through their use in law enforcement that their aggressive tendencies have also gotten attention, and being such large and powerful animals, some insurance companies will factor that into their price.