The Ashera Cat
The rarest domestic cat available is called the Ashera (TM) and is a cross between a domestic cat and an Asian Leopard Cat like the Bengal Cat, but also is crossed with an African Serval.
At between $22,000 and $28,000, you do get an amazing looking cat!
Best viewed large.
Edit Nov 09 - It seems that the so called breeder of this breed is a fake and the cats are in fact Savannah Cats - ashera-savannah-cat.blogspot.com/