Well, there are a lot of them and no doubt I'll list more when they come to mind but for my mind there is no contest for first place. As far as I know there is only the one public photo of it, and outside of a few interested parties the general public could not name it. It is of course the Aquarius.
One of the first true spacecraft, she never fulfilled her mission. Instead she did something she was in no way designed to do: took three men safely through the vacuum of space around the moon and returned them safe to earth, sacrificing the last of her power to reanimate the lifeless Odyssey. She reentered at much the same time as Odyssey and of course without a heat shield burnt up, somewhere over Fiji.
She was IMO the finest ship ever to fly.