The following is a list of reported 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.
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology