OK, yes, I understand that the main ship of the series is one that (as a male viewer with a brother) I'm rather inclined to recoil from. But I really, really don't see Dean/Sam. And I could hardly care less about RPF (nothing against it, just not my thing), so the Jared/Jensen angle does nothing for me. So I'm basically apart from the major parts of the slash fandom for this series due to personal taste.
On the other hand? There are certainly a few ways I could see bringing some slash up in here. Dean/Castiel, sure -- that one even seems to have the actor behind one of the characters on board, if in a somewhat tongue-in-cheek manner (which is how I'd tend to see Dean/Cas working anyway).
More seriously than that, though:
Bobby/Rufus and/or Bobby/Crowley. Much more tension to work with, IMNSHO. (And, of course, Crowley/anyone, but that pretty much goes without saying.)
Now, at the same time, none of this really takes away from the general air of machismo and Eurocentrism that so many people have pointed out. So call Supernatural a guilty pleasure.