My favourite is still the Contax G1/G2 with a Zeiss Hologon 16 f/8
The lens is fixed at f8. So, it gives a new meaning to "f/8 and be there"
The Planar 45 f/2 is also a really cool lens, and with the autofocus, you never have to really look through the RF to focus (not like you really need to with the DOF of the 16mm Hologon).
Of course, one of the twin-lens Minox replicas would be cool as hell too, if you had the patience to work with the tiny negs.