My favorite is when you have a 5 or 6 move checkmate combination and they play it to one move before checkmate and resign. I've always loved that. As a subscriber I don't care if they milk the clock though. What I do hate is when they drop 400-500 ratings points before the game times out. Somehow that seems unfair.
Well, that happened to me too. But I wasn't expecting to beat the guy at all, so when he resigned (he resigned a whole bunch of games at once) and his rating slipped, it would have been churlish to complain. He has to work much harder to regain his rating than I do to make the points I would have gained.