Intel
Socket 423 PGA
Socket 478 PGA
Socket 775 LGA
AMD
Socket A (462)
Socket 754
Socket 939
Socket 940
This is the recent list of sockets for the average consumer.
About the pin count, the easiest way to say it is this. A higher pint count enabled more I/O (Input Ouput) Operations, in other words, more communication to the rest of the system. If your not overclocking, then it does not matter which socket you go with LGA 775 or PGA 478. Whatever one floats your boat!!!, Prescott is the only LGA supported CPU. Socket 478 swings both ways, Northwood and Prescott. If you want under 3.2 GHz, then get a Socket 478 board with a Northwood Pentium 4. If you want above then go with LGA.
You want bang for buck, get a Athlon 64 Socket 939 processor.