Yeah, it was TechTools Deluxe. I couldn't say why Apple stopped carrying, but Micromat sells the Pro version. You can use the built-in Apple Hardware Test by booting up holding the D key. On older Macs you needed one of the install discs in the optical drive, but newer Macs boot to the test without it (I guess it's on a hidden partition or the Boot ROM, etc.).
I don't think TechTools is necessary. Even if it found a problem, would you be able to fix it yourself?