intel processors come in all shapes and sizes so i'll try to be brief by discussing only the ones that are current on the market.
The market for intel processors are currently divided into 2 sides. One side if for single core processors while the other is for multi-cores.
Single cores:
Pentium 4, pentium m, celeron, core solo (not very common)
these cpus are single cores meaning that they only have one processor. They are relatively cheap compared to multicores. The difference between these are clock values, hyper threading, 64 bit support, and fsb. Pentium 4 and celerons are cores found in desktops while the m is found in laptops. Single cores generally have low fsb but high clock speeds. Think of it as having a lot of water pressure but only a straw to dispense it. That's how fsb and clock values work. So single cores should provide you with a lot of raq power but they're not good at multi-tasking or jobs that requires it divide it's attention. Games like crysis will be better with multi-cores because the pc has to generate so many different things at once while focusing on countless calculations and processes. The hyperthreading support does help the single core pentium 4s with multi-tasking but it's not as much as multicores. So if you're just looking for something with a lot of raw power. These are for you.
Multi-core
core duo, core 2 duo, core 2 quad
these are multi-core processors developed by intel. They are used in both laptops and desktops except for the quad. It's used in desktops only. The first 2 processors are dual cores while the last is quad cored. These processors have a high fsb rating and generally lower clock speed. So you have to be careful when looking at these. The high fsb means that the system does really really well with dividing and transferring it's processing power, but if you get a low clock speed then there's not enough power to begin with for the assignment. Example you may have a large hose but if you have low water pressure.. It's useless. That's why multi-cores are great for the modern pc user who multitasks way too much but if it's under 2.0ghz in clock speed. You should be worried about not having enough raw power to get you through intensive work. Multicores generally cost a lot more than single cores since they're relatively new technology. Btw the core 2 duo is faster than the core duo by about 7%. Meanwhile the quadcore is the ultimate in processor goodness but costs $400+.
I hope these facts helped.