There are 2 main manufacturers of processors for personal computers. These are AMD and INTEL.
The basic ranges of processors available are :-
Intel
Celeron - This is an entry level processor often found in cheaper computers. This is designed to compete with the amd sempron ranges.
Pentium 4 - These comes in a series of ranges from entry level to high end processors. Only available in single core.
Pentium D- This is the dual core version of the pentium 4. They are a cheaper version of core 2 duo. Often found in cheaper "dual core" personal computers. Performance is not up to the standards of core 2 duo.
Core 2 duo/Quad - These are the "proper" twin/Quad core processors. These are in tests currently the fastest processors overall. They are significantly more expensive than the pentium D but offer far superior performance.
Xeon - These are Intel's "Professional" range and like the core 2 come in duo or quad core processors. The overall performance is similar to core 2 duo/quad. They are designed primarily for servers and the Mainboards to run these are considerably (2 to 4 times) more expensive than core 2 mainboard's. The big advantage over the core 2 however is than you can run several of these on one board. For home computer use where only a single processor is required then core 2 is still the best choice for the price. If however you want to build something to rival the ASCI Red Supercomputer (10,000 Pentium Pro's running a trillion calculations a second or 1 terra flop) and have a few millions pounds to spend then maybe this is for you.
Intel also produce a range of laptop processors with low power consumption in celeron/pentium and core 2 ranges.
Intel I7 - The new Intel range of I7 processors currently consists of 3 different models(The 920,940 and the 965). These use a new socket LGA1366 and are fabricated on the new 45nm wafers.
Future Intel - intel are currently testing an 80 core proof of concept processor which has the ability to run at 1 terra flop. This is the size of an average fingernail and consumes a mere 62 watts of electricity. The ASCI Red Supercomputer with similar performance consumed 500 Kilowatts and took up 2000 square feet!. The new Tylersberg server chipset and nehalem-ep server should be out as you read this.
AMD
Sempron - Sempron processors come in either 32 or 64 bit processors and are a cut down version of the amd athlon. They are designed to compete with the Intel Celeron range.
Athlon - Athlon processors come in either 32 or 64 bit processors and dual core varieties. They are designed to compete with the Intel range from the pentium 4 to the pentium d dual core processors. Speed wise they are in tests faster than the intel range in gaming applications. The AMD Quad FX platform is a two-socket, four-core processing solution featuring Dual Socket Direct Connect (DSDC) Architecture for high-bandwidth processor to processor communication.
Opteron - The Opteron comes in a variety of range from single to quad core. They are designed to compete with the intel core 2 duo and xeon ranges. Like the xeon multiple processors can be used on a single board up to a current maximum of 16 cores. In tests they lag behind the Intel range and the high end ones are quiet expensive.
Phenom - The phenom and Phenom2 processors are aimed at high end gamers. they come in dual, triple and quad core versions.
Future AMD - Amd have recently purchased ATI graphics and are working on integrating a cpu and a gpu(graphics processor) on the same chip. This should dramatically increase game performance as the 2 chips can talk to each other at a very fast speed. | 
