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. SpeedFan can even change the FSB
on some hardware (but this should be considered a bonus feature). 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. Several sensors, like Winbond's and the AS99127F support fan speed changing, as well as others from Maxim, Myson, Analog Devices, National Semiconductor and ITE, but the hardware manufacturer must have connected the relevant pins to some additional, yet trivial, circuitry. This means that if you have, say, a Winbond W83782D on a BP6 then you're ok, but not every motherboard with such a hardware monitor chip will be able to change fan speeds. From one of the very first hardware monitor chips that could be found in standard PCs, the National Semiconductor LM75 (and all of its clones, like the Philips NE1617 and the Philips NE1618 or the Maxim MAX1617) or the Analog Devices ADM1021, such chips have been greatly improved, both in their precision and in their capabilities. Current chips can monitor fan speeds, voltages and change fan speeds by using PWMs (Pulse Width Modulation). Some chips can even be programmed to vary fan speeds without any additional software intervention. If your BIOS was programmed to setup such chips this way you can still try to use SpeedFan's Advanced Configuration to revert to manual (software controlled) mode. Winbond W83697HF, Analog Devices ADT7463, SMSC EMC6D102, ITE IT8712F, National LM85C and Maxim MAX6650 are very good candidates. Some SuperIO chips include temperature sensors too. SpeedFan can automatically detect them and use their features. SpeedFan can find almost any hardware monitor chip connected to the 2-wire SMBus (System Management Bus, a subset of the I2C BUS) Serial Interface and to the ISA BUS and works fine with Windows 9x, ME, NT, 2000, 2003 and Windows XP. It works with Windows 64 bit too. It can be minimized to the tray and is compatible with Motherboard Monitor 5.
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Chris Down 
Saxtus 
Excellent program. Bear in mind that this program doesn't filter out the gibberish results that some sensors give, you have to work out those for yourself. This program just outputs the data, it makes no assumptions about what is connected to where.
best to view our computer temperature
My dad who works in computer programming for HP told me to get this software when I was having heat issues on my Dell before I got my HP laptop. The features on it mostly don't work on my machine, and that's fine, I just use it to keep an eye on my system temperature and know when it's getting too hot for what it normally runs at and to adjust it, turn up the fan, or even shut it off and let it cool. It's a great way to get a better feel for your machine and what it needs.
I would recommend this program to friends.
One person told me not to trust it...but I beg to differ.
great to control the heat of the system
la mejor utilidad al rato de controlar la temperatura de tu pc tando de la fuente como del cpu.
the best use of time to control the temperature of your pc ing the source and the cpu.
a melhor utilização do tempo para controlar a temperatura do seu pc ção da fonte e da CPU.
最有效地利用時間，溫度控制你的電腦技術的來源和CPU 。
la mejor utilidad al rato de controlar la temperatura de tu pc tando de la fuente como del cpu.
the best use of time to control the temperature of your pc ing the source and the cpu.
Chill !
changing fan speed is cool
A good piece of software for core temperatures and fan speeds
Reliable software to check fan speed and temperature
Great application.
Its great for monitoring temperatures but crap for overclocking because it hadly supports any motherboards :(
sure would like to know how the logging works since i'd like to see the last temp before the laptop crashed from overheating..
An excellent little app that will keep things cool without hoggin up your memory especially nice for laptops