For stress-testing from a custom live CD, I use folding@home, seti@home, memtest, and cpuburn. Memtest is now included on the newest Knoppix. There are also some disk benchmarks- bonnie++, dbench.....

You can download seti or folding into your home directory, chmod +x it, and then launch it, from any live CD.

http://overclockix.octeams.com