Just noticed a new version of memtest86+ is out! Version 1.70 is out (finally) with support for a lot of the newer hardware. (Been waiting for this release for ages)

Quote Originally Posted by memtest86+ 1.70 Changes
  • New Features
    • Add new DMI polling feature
    • Add Support for Core/Core2 Solo/Duo/Quad CPU
    • Add Support for AMD K8 with DDR2 Memory
    • Add Support for Intel CPU with 192/384 KB L2 Cache
    • Add Support for FB-DIMM based memory (DMI)
    • Add Detection for ALI CyberAladdin-T (M1644)
    • Add Detection for Turion 64 X2
    • Add Support for ATi Radeon xPress 3200
    • Add Support for Intel i975X
    • Add Support for Intel Q965/P965
    • Add Support for Intel Q963/Q965
  • Bug Fixes
    • Force detection for AMD K8 with unknown chipsets
http://www.memtest.org/