I have a supermassive black hole that achieved a stable orbit in my laundry room. It eats my socks to make up for mass lost to evaporation.
Other than that I would guess my wife’s old timey desk. It’s a 50’s institutional thing.
Not that my wife is that old btw, we bought it second hand.
You know, before I clicked on this thread, I bet myself a doughnut that* that * answer would be in the first five replies. I reckon numero uno means I owe myself two doughnuts. 
Cafeful with them donuts or YOU’ll be the heaviest thing in YOUR house. 
My father’s '69 Buick.
(And it’s kept in the basement, so yes it’s inside the house)
Good call–it’s a tossup between me and the fridge. My dining table is substantial as well.
Almost certainly my refrigerator. Of the things I moved into the house myself, probably my dual recliner sofa.
An entertainment center, solid oak. But it disassembles into pieces for moving, so I’m not sure if that counts. Other than that, probably the fridge and the oak desk, in that order.
Either the piano (spinet) or the fridge; I’m betting they’re pretty close in weight.
The collective bookshelves with books would outweigh them both, though.
Right now it’s my Delta Unisaw, shipping weight was about 500lbs.
Until a few months ago it was 11,500lbs of AOL CDs in Rubbermaid garbage cans.
So, are you AOL?
My husband’s discography.
OK, my piano. It’s a Victorian upright grand and it’s solid mahogany. Prolly weighs, uh, a lot. 750 pounds, I’d guess.
Kind of the opposite, I was half of the “No More AOL CDs” team.
The Hot tub (550 gallons), but it’s outdoors. In the Garage, a south Bend 10 Heavy Lathe, 1100-1200 lbs.
I’ve got one car on a lift above another car, they’re not officially included, but I bet it’s a pretty good load on the concrete.
You sure it’s not those two humongous brass balls you’re lugging around? They’re appearing to be pretty massive right about now.
My house? Upright piano at one time. I’m guessing the chest freezer right now though.
I imagine it’s the woodstove.
Yeah, so I came in here to say, ‘‘Sartre’s Being and Nothingness,’’ but you know, whatever guys.
grumble grumble THE BED grumble grumble
Probably my waterbed.
My grand piano weighs 799 lbs, according to the specs.
BTW, Cluricaun, I sold my last big, heavy 35-inch tube TV on eBay, with the proviso that the buyer had to come and pick it up (and that I wasn’t going to help with the moving). I’ll probably do something similar with my current big, heavy rear-projection TV when I buy a new flat-screen in the next few months.
The obvious advantage of eBay over Craigslist is that the competition for the highest price happens automatically, so you’ll probably get a higher price, you don’t have to deal with as many back-and-forth e-mail questions, and you’re less likely to have the buyer back out of the deal at the last minute.
My two cents.
I was going to mention that the built-in chest of drawers is infinitely heavy. But I’m sure I’m mistaken about that.
And reading other entries makes me think maybe my fold-out sectional couch is the heaviest item.
Don’t jump to conclusions. Do you find that other objects (the cat, for instance, or the Canis Major Dwarf Galaxy) are drawn toward it?