There was another thread about this previously.

But anyway:
1. Flashing the bios
2. Flashing anything else (video, HD, CDrom can be flashed in most cases)
3. Consuming printer consumables etc
4. Any commands to the CPU/mobo to cause it to overheat - unlikely to be effective, most CPUs will stop making heat once they get so hot they crash
5. wearing out FDs, CDROMs by physically moving too much.
6. Seeking devices beyond the end, breaking the mechansim. Only generally possible on CDs and HDs if you reflash the device software to do this (not directly controllable from host). Some floppy drives can be killed this way though.
7. Making a picture on the monior which causes it to "burn" the screen. Not possible on most modern monitors
8. Making a very loud or high noise which blows up speakers (or causes human to destroy them out of annoyance)
9. CDRs - giving the write command on non-writeable discs, or discs which are already written - most models would require reflashing to do this.

Slarty