Speedfan - Monitors fans / voltages, etc

Meant for the power user, so be careful.
SpeedFan is a program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. SpeedFan can even access S.M.A.R.T. info for those hard disks that support this feature and show hard disk temperatures too, if supported. SpeedFan supports SCSI disks too.
At the lowest level, SpeedFan is a hardware monitor software that can access digital temperature sensors, but its main feature is that it can change fan speeds (depending on the capabilities of your sensor chip and your hardware) according to the temperatures inside your pc, thus reducing noise.
SpeedFan monitors temperatures, through available hardware monitor chips which expose their temperature sensors connected to different places inside your computer, and, according to your setup, does its best to keep them at your desired value. You can even change a fan speed according to the temperature of your hard disk. When choosing parameters for the minimum and maximum fan speed, try to set them by hand (disable all the VARIATE FANs checkboxes) and listen to the noise. When you hear no noise from the fan then you can set that value as the minimum fan speed for that fan.

Available at this link.