Spike and Angel, President Roslin and Gaius Baltar, Harry and Hermione—shippers often find pairings that the original author might have overlooked. What coupling of fictional characters would you most like to see?
Oddly enough I've been on a bit of a crossover fanfic binge recently. Obviously this is an area where personal mileage varies (a lot) but I have to say that some of the shipping that goes on makes me go "ewwww". I've seen enough of this recently to have a personal rule: stop reading as soon as it goes beyond the ratings level of any contributing universe.
Another problem for me with shipping is that the fandoms I might be interested in reading about usually have well visualised relationships that are firmly grounded in the characters. So messing with those relationships tends to trigger a "No, no, no! X would never do that! And Y would run away!" reaction. This tends to kill my interest in that story stone cold dead.
I did run across a fabulous, if regrettably unfinished, BtVS/Firefly crossover that made better use of Xander than much of the original material did. It didn't seem to be shipping Xander with anyone though.