The belief that animals have long since carried the ability to communicate with nature and spirits has made the use of a familiar(s) popular in the practice of witchcraft. Crows were and still are especially popular in Black Magic because it is believed the Crow is the guardians of the soul of the fdead. They have been used in conjuration and divination magic for hundred of years.
Cats are an alltime (and my personal favorite) favorite for as far back as the Ancient Egyptians who worshipped cats. This was apparant in the Egypsian Deity Bastet. Any animal can be a familiar depending on your personal bond with the animal of your choice.
Below are a few of mine: Hosted by Picassa.