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

iStat is an advanced Mac system monitor for your menubar.

Real Temp is a temperature monitoring program designed for all Intel processors.

Hardware Info (HWiNFO) is a powerful system information utility designed especially for detection of hardware.

HWMonitor is a hardware monitoring program that reads PC systems main health sensors : voltages, temperatures, fans speed.