Let's see... there's been so much dead hardware over the years:
Commodore Plus+4 - dropped a screw on the motherboard while it was on
Celeron 600 and ALL associated components - HD, RAM, Motherboard, the works. Left it in a cabinet running, accidentally closed the door, came back to a horrible burning smell...
Tyan Tiger S2460 AMD DP motherboard + RaidMax 550w power supply. Don't know which one went first. Several chips on the motherboard achieved liftoff and the power supply caught fire. Out of warranty, too...
Asus A7M266-D AMD DP motherboard + 350w generic power supply. Powered on, running some heavy apps, powered off. Never powered on again. PS died, MB no longer POSTs...
Duron 1700 - dead out of the box. RMA'd to Newegg.
Seagate 4 GB Barracuda HD (1.6" 50pin SCSI) - BIG chunky hard drive. Worked from the day it was manufactured (around 1994) to 2003, then died of a head crash.
Maxtor 20 GB IDE drive. Had some weirdass problems - it would "work" with a sustained R/W transfer rate of 100 KB /sec. Yes, my internet connection was faster. Ran the Maxtor diags on it, it passed. Banged it against the table while running the Maxtor diagnostics, it failed. RMA'd with the produced error code.
PowerColor Radeon 8500. Interesting graphical artifacts, then it sort of stopped working. RMA'd.
ECS K7S5A - not mine, but my friend put a standoff through a SMT capacitor on the bottom. Oops. I soldered a new one on, and it sort of worked - you had to power it on and off about 30 times before it would pass POST and boot, but once it booted, it was rock solid....
Some random P1 motherboard - stepped on it. Oops.
Many, many power supplies - a combination of overheating and overloading.
One power supply in particular stands out. I had a PS set to 220, plugged it into a 110 line. This PS had no lid and no fan, so it was easy enough to see inside. Hit power on the computer (spread across a table). The CPU fan kicked over once, and the power supply burst into flames.
Far more than my fair share of Linksys NICs, and a few generic RTL8139 NICs. They just stopped working. Not a particularly interesting way to go...
Belkin Omniview KVM switch - 4 port PS/2. This is when I discovered that the port on the back of an SGI Iris Indigo, that looks suspiciously like a PS/2 port, is, in fact, not. It is decidedly incompatible with PS/2 devices. Plugged the KVM switch in to the Iris Indigo, powered it (Indigo) up, and SNAP! Black smoke poured out of the KVM, and it made an ungodly shriek (from the beeper).
Seagate ST39102FC 9.1gb Fibre Channel drives, qty 2. I built a custom interface board for the 40-pin SCA2 connector on the back of the drive, and plugged it in. "Oops, I seem to have crossed a power and ground line," I say, as the drive's logic board explodes in a plume of smoke. Then I did it again, because I wasn't paying attention and picked up the original interface board instead of the newly rewired one.
I'm sure there are more....