Sleek upper body, soft yet defined muscular features, goat legs, short tail, no shortage of curly hair and horns on the head.
But really...
I've found that my preference has always changed based on the personality. While I can find any male body aesthetically pleasing in a non-sexual way, for it to become sexual the personality has to be just right. I've found that it's generally the skinnier, odd, small, and nerdy types of guys that have the personalities I like, which, thanks to the internet, I've often found after the fact.
Still, a model man build is undeniably nice to look at, as if all those signals my brain is built to search for are realized with perfection. The statue of David is a good example of this, which I think shows that it can also transcend generation trends. After all, men still like boobs, right? The difference here is I don't get aroused by the pure visual appearance -- dude's gotta have a nice pair...of brain hemispheres.
Incidentally, I just noticed Autechre's "Stud" was playing when I posted this. Awesome.