Tiger-Tech.ca Systems Basic CPU Buyer's Guide

For the average home/business PC system here are the rankings (top is best/newer CPU):
Intel iCore 7 (3rd-5th gen)
Intel iCore 5 (3rd-5th gen)
Intel iCore 3 (3rd-5th gen)
Note: There is some overlap between the 1st and 2nd gen iCores with older Core2 Duo CPUs.

Intel B-series CPUs (in notebooks for value)
Intel G-series CPUs for value

Intel Core2 Duo
Note: Some higher end Core2 Duo CPUs were actually faster than some 1st gen iCore i3/i5 and even some i7.

Intel Core Duo

Intel Dual Core

Intel Pentium4 with HT (Hyperthreading)

Intel Pentium4

- Intel Core Duo CPUs out-perform the AMD Turions & Intel Dual Core overall, the Core 2 Duo CPUs are even faster.
The Intel iCore i3 CPUs will outperform all but the top half of Core 2 Duos.  The Intel i5 CPUs will outperform all but the top Core 2 Duo CPUs.
The Intel i7 will outperform nearly all previous Intel CPUs.  The second generation iCores are a bit faster, third to fifth generation are faster yet.  
The Intel B900 series are almost as fast the iCore3 but only for notebooks.  Xeon CPUs are more for server or heavy use.
Once again Intel (from the P4 to present iCore processors) are still faster than AMD ones.  Although AMDs may be a bit less expensive - the value really isn't there.

Some CPUs have quad or more cores for better performance but you need a 64-bit Operating System and 64-bit programs that require this extra processing power.
There are other factors such as processor speed, amount and speed of cache memory, and number processing cores.  But this excludes other factors 
such as the other components in the PC or notebook like amount of RAM, the video, or use of multiple CPUs.

Today's CPU are harder to compare directly as various models have been introduced.  However, most Intel CPUS that
are not the B900 or iCore series are actually much slower.

If you want more info and real test results - see Tom's Hardware CPU Benchmarks.
and Passmark CPU Benchmark.