That is a HUGE question, and is very open to interpretation and subjective opinion.
Parasitology I like Georgi's
Anatomy, I like Pasquini and Millers Guide to the Dissection of the Dog
Physiology, Nothing beat Guyton, but that is for Human Physiology, Dukes Physiology of Domestic Animals is a great additional resource, but I find the readings and diagrams incredibly dry, and wouldn't recommend it as a sole book.
For histology, any old book would do IMO
Pathology, Don't know the name, but its a HUGE book, called Pathology for Veterinary Students or something (its not in front of me, but I will edit it in at a later date).
Umm... thats about all I regularly use, other then that I just learn from provided PPT's.