There are a myriad of single shot actions...heck there are a sea of all kinds of actions.
I now seem to favor single shots with external hammers. I think that Ruger No.1's are probably the best there is from a sleek and practical view. However, I have come to like the looks of the Sharps and Winchester 1885. I don't think the Remington Rolling Block is quite as attractive.
The Martini-Henry is awesome. The Sharps Borchardt is neat but clunky in comparison.
What's your favorite?