As for me, there is one that I am totally obsessed with.
It is a monster to create very little image of all the big things and in every sense, is an engineering miracle.
"Nikon 6mm fisheye"
At one point I believed this is another creation of those guys who made a movie in a dark room, calling "Man walking on the Moon" and wanted us to believe man actually has walked on the moon!
Well my paranoid is all gone now after seeing 3 of it for sale so far in past 8 years on ebay.
As per history
(A good review exist here) this was made only by special order and only few are actually made. Three were shown in USA as display in major cities and one, in Chicago that was on window display, was ran into by a car and it disappeared with no trace!!!
At above 5 Kg weight, this 24 cm in diameter, non-AI fish eye F/2.8, 12 elements in 9 groups lens with amazing angle of 220 degree that means not only sees and record anything in front of it (180 degree in x and y axis), but it takes extra look to what is behind it, so the legs of tripod and photographer behind and form other end, head of photographer are all in the field of view of picture. I hope by giving the info here, I am not adding more competitors to hunt on of these baby s but I really first like to share the knowledge and then learn if any one of you actually has seen or touch it real world. As for now, sweet dreams for me. Truly this is best to be kept in a museum if you can find and donate it to place of your interest.
This is the picture of last one that I sadly witnessed getting sold twice on ebay and couldn't afford it (Well divorce will cost me a lot more...). I hope I am not in breaking of any applicable laws by uploading this imformative image as the ebay auction is gone now and pictures do not exist any more so I can't quot the auction number.
[img=http://img148.imageshack.us/img148/1826/nikon6mmmf3.th.jpg]