Off hand, I'd guess the refrigerator -- I know it's a pain in the butt even for two people working together to move it. I have no idea what the actual weight is, though. A close runner up would be the 32" tube TV that my parents handed down to me after buying an HDTV. That sucker must weigh 200 pounds, and just moving it the 6 or so feet from the hallway that we left it in after getting the HDTV to my bedroom was an ordeal.
Edit: That's for my home. For the on campus apartment that I live in at school, that would be my guitar amp (which weighs 50 pounds) or, if it counts, the box that I put all of my clothes in on laundry day. I haven't specifically weighed it, but my estimate is well over 100 pounds, fully loaded.
Edit Edit: The apartment also has a refrigerator, and it's one of the old style steel box versions that were everywhere during the 90's. That thing has got to be heavy, although I've never had to move it.