I have been using the Ultime Boot Disk for the past few months to test x86 and X64 hardware. The disk contains numerous awesome utilities that can be used to test memory, disks and CPUs. The following packages come on the CD, and are four of my personal favorites:
Memtest86+ to test memory
Darik’s Boot and Nuke to securely erase data from a disk drive
CPU burn to test CPUs
PCI sniffer to identify the type of card in a system