Early 105mm f2.5 sonnar
I've shot with some east and west german zeiss sonnar type lenses in the past (notably the CZJ 180mm f2.8 and the western zeiss 150mm f4 on 6X6 film) and always loved the look from them. So I hunted down an early chrome barrel 105mm f2.8 non-Ai lens and then sent it off to have it Ai'd. I was out in the backyard today shooting some dogwood blossoms and I can tell already, this is going to be a great lens.
I don't doubt the later versions are probably sharper and more flare resistant (and some have a cool built in hood), plus they wouldn't have to be converted to work on a modern camera, but the way this lens draws is really nice.