This has been an addition to my 3 computers for some time and won't do without!
From the Authors:
Core Temp is a compact, no fuss, small footprint program to monitor CPU temperature.
Now Windows Vista and Windows 7 ready! (x86 and x64)
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.