The Cell Processor is STI's(Sony,Toshiba,IBM) new processor, an attempt to revolutionize a new type of processor i guess. As for the PS3, it consists of 8 cores, but only uses 7, that last one being for other purposes.
For more information that, heres wikipedia! http://en.wikipedia.org/wiki/Cell_processor
As for the XBOX 360, Here's Wikipedia again mainly at the Xenon processor!
Central processing unit
The Xbox 360 takes a new approach to hardware compared to its predecessor. The CPU, named Xenon at Microsoft and "Waternoose" at IBM, is a custom triple-core PowerPC-based design by IBM. The CPU emphasizes high floating point performance through multiple FPU and SIMD vector processing units in each core. It has a theoretical peak performance of 115.2 gigaflops and is capable of 9.6 billion dot products per second. Each core of the CPU is simultaneous multithreading capable and clocked at 3.2 gigahertz. However, to reduce CPU die size, complexity, cost, and power demands, the processor uses in-order execution in contrast to the Intel Coppermine128-based Mobile Celeron used in Xbox which used more advanced out-of-order execution. The original chip uses a 90 nanometer process, although a 65 nanometer process SOI revision was originally planned for early 2007, but it has been delayed until mid-2007. A 21.6 GB/s front side bus, aggregated 10.8 GB/s upstream and downstream, connects Xenon with the graphics processor/northbridge. Xenon is equipped with a 1 MiB Level 2 cache on-die running at half CPU clock speed. This cache is shared amongst the three CPU cores. The CPU also contains ROM storing Microsoft private encrypted keys, used to decrypt game data. The heat sink implemented to cool the CPU is composed of aluminum fins with copper base heat pipes. The heat sink is cooled by two 60 millimeter fans at the back of the console.