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)...

This topic has come up in the past, check here :
http://www.fredmiranda.com/forum/topic/752390/0

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.

5D + Nikkor AF 180/2.8