The Ep of Futurama from the latest season where Fry enters his memory to go back to the last day before he was frozen, then never wants to leave his house. The end of the episode where Nibbler rewards him by allowing him to enter his mother's dream and have one last goodbye with her kills me. Having lost my mum when still quite young it really hit home.
One that unexpectedly choked me up was Planes, Trains, and Automobiles. At the end when Steve Martin realises that John Candy doesn't actually have anyone to go home to and Candy reveals his wife died, heartbreaking stuff.
For some reason comedies that know how to throw a well timed emotional curveball have a much higher success rate at making me tear up than dramas.
Oh, and one last one. "Bart gets an F". When Bart starts crying at the end and declaring that he really did try this time and is just stupid....