I used RAM Probe. I believe its a newer version of Memtest86+
"RAM Probe (formerly OTCOMP Memtest 86+) is a free memory testing software suite designed to diagnose your RAM for faults.
Our code is an updated fork of the memtest86+ project maintained by some members of the french hardware site x86-secret.com. It in turn is based on the original memtest86 v3.0 written by Chris Brady of Silicon Graphics, Inc. See the original websites for more information about the tests performed. Our primary updates include detection for over 75 additional chipsets plus various other features/fixes (see changelog info for details)."