Just a few years ago, the job of tracking Intel and Advanced Micro Devices price cuts was a lot easier. Each company only had around 15 or so processors on the market at any given time. Intel cut prices once a quarter and AMD followed a few days later after they got their hands on Intel's new price list.
AMD would also negotiate sweetheart deals with large customers, so that the retail price of its chips were often lower than the "official" wholesale price.
Now, processor models have proliferated. AMD has 93 chips on its price list, and Intel lists 159, including Centrino bundles. (I may have missed a few in there, but you get the point.)
In any event, Intel cut Pentium 4 prices by 29 to 21 percent. The Pentium 4 670, which runs at 3.8GHz and comes with a 2MB cache, dropped from $851 to $607. At the low end, the 630, which churns at 3GHz, went from $224 to $178. More cuts can be found here.