CPU-Z is a diagnostic tool that provides information on your CPU, including: processor name and vendor, core stepping and process, processor package, internal and external clocks, clock multiplier, partial overclock detection, processor features, supported instructions sets, L1 and L2 cache information, location, size, speed, and technology.
Not to forget, its a very nifty tool, since its very small in size, and very handy when one of your cousins says they want to upgrade, but dont have a clue on what system they have.