SpeedFan is a program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips.

MSI Afterburner is a graphics card overclocking utility which gives you full control of your graphics cards.

RivaTuner is a freeware overclocking and hardware monitoring software.

AIDA64 is a system information, diagnostics, and auditing application.

Prime95 is the freeware used by GIMPS, a distributed computing project dedicated to finding new Mersenne prime numbers.