This is a picture of a dog-fox hybrid in the Grosvenor Museum, one of the few known museum specimens.
The following is a list of dog crosses discussed on this site. Some of these crosses are much better documented than others (as indicated by the reliability arrow). Moreover, some are extremely disparate, and so must be taken with a large grain of salt, but all have been reported at least once.
Most shared on Macroevolution.net: