I once lived in a house with aluminum duct work, which was exposed in the basement. I pulled the vent cover off in my room, stuck a mic in the vent, then ran to the other end of the house with a drum stick and banged the crap out of the vent. Great sample. Still using that one.
Similarly, try putting a guitar cab at one end of the ductwork and a mic at the other for some narrrrrrrrrrsty 'verb.
Also, I've mic'd a guitar cab with different sized cardboard and metal tubes between the amp and mic. Mixed together, they give a kind of hollow, phase-shifter-standing-still kind of tone.
Finally, if anyone ever comes to your home to do any kind of maintenance or construction work, slip a discrete SDC somewhere nearby and record as much of it as you can. Wonderful source of thumps, bumps, klanks, squeeks, slams, and other such noises, not to mention great vocal samples.