yep, although i love nikkor 180/2.8D ED, but no optical diff between the two as far as i know...
ended up with 4 180mm (nikkor, cz 180/2.8, leica 180/2.8 and leica 180//3.4), don't even know why i keep all of them, the two most often used are nikkor 180/2.8 (on nikons) and leica elmarit 180/2.8 (on canons)
Surprised nobody has mentioned the Voigtlander 180 f4 APO. Tiny lens (smalest option by far), very sharp, great colour and bokeh and reasonably priced.
I've noticed that in the past 6 months Nikon prices on Ebay have jumped 30-50%, so if you're thinking of Nikon, don't wait too much longer...and I would expect Olympus lenses to jump now too (with the release of the new RF that will take the OM lenses with an adapter)...
All the lens have have now been mentioned and it really depends on what you will be using it for and how much you want to spend.
I love my Leica 180 APO 2.8 which is very sharp even at f2.8 is still very good with Leica 2x APO extender if you want more reach.
Carl Zeiss Jena Sonnar 180mm f2.8 either P or M42. A HUGE beast of a lens, but from what I've seen, it does deliver - especially for the (reasonable) price.
