Sharp PC 1403H from '91. I'd bet money that my 1986 Sharp PC 1402 (same device with less memory) still would be working too if I hadn't sold it.
Batteries are from the 90ies too - haven't replaced them since. Still work. Still have microcassettes with my own software on them, such as a Shadowrun (1st Ed.) Character Builder. Would print out the stats on the cash register strip printer. Still have that too, still works.
My Mac Mini from 2006 still is going strong, aswell as my HTC Desire HD Smartphone and my HTC Flyer tablet, both of which have been in hard everyday use since 3 and 2 years ago respectively. Both have been dropped hard multiple times, the Flyer is nicked and dented around the edges, the pounch looks like it's been through a war and I've wasted 3 hardcases on my HTC Desire HD and replaced the battery and protective foil once, because it was so banged up already. I expect both to last another few years with everyday use. It's a shame replacing the HTC Flyer battery isn't done as easyly as with the phone.
I consider the HTC Desire HD and the HTC Flyer the best smartphone and tablet enclosures ever (solid aluminium), better even than Apples current cases - although the iPad Air enclosure does look cool. Shame they don't build them in that quality anymore. They are from a time when everyone was rushing into the mobile market and trying to make a name for themselves. Although the HTC One line still has pretty goog enclosures.
Interesting tidbit: The HTC Flyers enclosure is top notch and very sturdy which makes it notably heavier than your usual 7" plastic tablet. That's actually a little downside.