Ad Offerman's Chiplist is plain, dry text all the way, and awesomely comprehensive. We referred to it frequently while writing this guide.
The CPU Museum is not to be missed.
Chris Hare's excellent PC Hardware Links has a lot more than just links.
If you liked our page, you'll love Great Microprocessors of the Past and Present. It's a single long, plain text document covering just about everything. No graphics, no fancy layout, just reams of fascinating detail.
CPU World is a new site that has grown very rapidly and already contains a vast amount of useful information.
From Russia, VLSI Microprocessors has information on a broad range of parts, not just X86. Alas, it doesn't seem to be maintained anymore.
sandpile.org is a treasure-trove of detailed information for programmers. It's devoted to raw technical information, there's no benchmarking, comparisons, or opinions. Much of it is beside the point for hardware junkies like us, but see for yourself.
The CPU Info Center is another plain-looking page with lots of information. It hasn't been updated for several years, which is a shame.
Not really about CPUs, but the Uncreative Labs IBM PC/XT Restoration Guide is good fun.
When it comes to current-generation CPUs, Ace's Hardware is one of the very, very few genuinely insightful sites. For some incomprehensible reason, they no longer provide general purpose business benchmarks, which is a great shame and detracts significantly from the site's utility, but it is still essential reading.
CPU manufacturer sites tend to be pretty boring in the main and the AMD site is no exception. It no longer features the wealth of useful performance information that it used to, but dig around: there is still some interesting detail buried there.
IBM Microelectronics is not as relevant as it used to be back when the firm was fabbing for Cyrix (which is a shame, as both sites had a lot of interesting stuff in the mid to late '90s), but IBM still have their illustrated guide to chip manufacturing which is worth hunting down.
Intel have a huge site, full of expensive graphic layouts and covering an enormous range of products. Alas, a lot of it is rather vacuous self-congratulation. (Well, most company sites are full of vacuous self-congratulation, but this one more so than average.) Intel never mentions its competition, usually only quotes its own internal benchmarks, and often leaves you feeling unsatisfied. But if you dig deep there is usually some excellent stuff hidden in amongst the window dressing — the Intel museum is good value. (Like the IBM chip manufacturing page, it gets moved around whenever somene decides to overhaul the site, but it seems to always pop up again somewhere.)