I'd have to say my current desktop. It has seen hell, and it walked through those flames as if it were a cool spring day. Why the desktop is awesome:
1. Ridiculous CPU overclock on air. 3.12ghz to 4.06ghz? Stable? Pretty ridiculous. Gotta love those Core 2 Duos.
2. A video card that has taken oodles of dust and kept on fighting. Also somehow powerhousing even Deus Ex 3 like it's nothing. Radeon 4870, rock on buddy!
3. A motherboard that has seen power surges, short circuits, horrible ventilation, massively overloaded, overclocked and rocks on anyway.
4. Once again coming back to the CPU, it has survived both the heatsink falling off the mobo (goddamn clips!), AND the fan getting stuck due to a stray wire, multiple times! It has hit 85C more than once because of it, and not only did it NOT ONCE crash, but it, combined with the mobo, gave me a beeping warning so I had the opportunity to fix it! And in the other case, it actually powered off to save the CPU, like it should! There is no reason for that CPU to be alive.
The thing has honestly been through more **** than any of my other PCs, and is somehow more stable despite it.
Honorary mention being my iPad, for simply doing goddamn EVERYTHING when I'm away from my computer. Full RDP with awesome mouse support? Check. Ability to play back transcoded video over the net, OR play damn near anything locally (h264, divx, HD, subtitles, it rocks them all). Battery life that is honestly so good that I forget to charge it for days. Easy enough that I can hand it to my grandmother and I don't have to teach her how to use it.
Only downside to my iPad is the lack of filesystem access. I don't care if they want to abstract that crap out for the average consumer, there should still be a way to do it for advanced users. That single thing alone makes SO MANY THINGS horrendously difficult.