Core Temp is a compact, no fuss, small footprint program to monitor CPU temperature.
The uniqueness of it is that it shows the temperature of each individual core in each processor in your system! You can see in real time how the CPU temperature varies when you load your CPU. It's also completely motherboard independent.
Intel and AMD recently published detailed, public information about the DTS (Digital Thermal Sensor), which provides much higher accuracy and more relevant temperature reading than the standard thermal diode sensors do. (How does it work?).
This feature is supported on all Intel Core and Core 2 based processors as well as the whole AMD's Athlon64 line of CPUs. For a full list of supported CPUs see the CPU Support List.
Note: AMD Phenom is supported, but it does not report absolute temperature. More on this in How does it work?.
Core Temp also has a logging feature, allowing a user to easily record the temperature of his processor(s) over any period of time, then the data can be easily transferred into an excel datasheet for easy graphing.
Core Temp works on Windows 2000, XP, 2003 and Vista (both 32bit and 64bit versions).