Regarding the attractiveness of penises - In my very personal point of view, I think there definitely is such a thing. Only when they're hard, though. Naked shots of men with flaccid dicks staring intently into the camera are more odd to me than sexy.
After having seen the Murakami exhibit recently I'd have to point to his "Lonesome Cowboy" as an example of an attractive penis. In the bizarre context, it's actually rather naturalistic, large but not overly so, looking rather real even as it ejaculates so impossibly.
NSFW LINKS:
http://www.uark.edu/campus-resources...owboy-1997.jpg
http://www.textesgais.com/images/cowboy.jpg