This week sees the addition of the 2.2GHz Northwood P4 processor to the price guide, but with my advice to hold off on buying it. While the 15% performance improvement it offers over the 2.0GHz P4 is nice (I'm not yet listing the 2.0a Northwood, as I didn't see many listings for it this week), I don't see it being worth paying more than 60% more for it. And with the similarly-performing 1.67GHz Athlon XP 2000+ costing about half the 2.2GHz P4's price, it seems like even less of a good value until/unless Intel cuts prices again. As far as P4's go, I'd still recommend the 1.9GHz processors as holding the 'sweet spot' of balance between price and performance. They offer most of the performance of their higher-clocked siblings, and do it at $112 cheaper than the 2GHz P4's and $340 cheaper than the 2.2GHz Northwood P4's (comparing OEM pricing on each).
While it's nice to see new additions to the price charts, particularly on flagship processors, it's mostly because it helps make the previous top-dogs more affordable. Given the premium you end up paying to have the "best of the best," it's almost impossible to recommend going out and paying so much more for a 2.2GHz Northwood P4, or even the cheaper 1.67GHz Athlon XP 2000+, when the next-fastest processors offer so much of the performance for so much less in price.
How about Intel and AMD prices on the same page? Here you have it, starting with high-end CPUs.