My case, power supply (120W... hehe), keyboard, floppy, and printer are all still original from the system when it was purchased in November of 1999 (manufacturered before that). Mobo, 2 HDDs, 2 ODDs, CPU, memory, etc., etc., were all added/upgraded/replaced in my various upgrade cycles. thinks I think the case, PS, and keybd, and printer are all that remains from the original system.
Of course, I still have a 486 and a 386 back at home (I'm at college), but they're just collecting dust and I hardly ever touch them even when I am home.
And there's another computer back at home (that actually gets used regularly) that's around the same age as this one and that's also gone through various upgrade cycles (though it retained much more of its original hardware)