Just a head's up if you are running newish Socket A platforms.
For those that don't know, the Athlon XP is going End of Life. It is unclear exactly what this means (as the Socket A Sempron may continue), but it does mean that current product lines will probably rise in price, and not become cheaper until they are hopelessly outdated.
The current Athlon XP Mobile CPUs are one of the greatest bargains in computing history. They plug into almost any motherboard that supports the Barton core, and have BIOS settable multiplier and front-side bus. They overclock like crazy (rarely less than 2.4Ghz), and in most cases provide the best x87 floating point performance available.
Check the reviews on NewEgg, or the article on the subject at
http://www.techreport.com/reviews/2004q1/athlonxp-m-2500/index.x?pg=1My 2400 Mobile 35W is running at 2.5Ghz@1.7V with a budget quiet heatsink - and the price is up $6 since I bought it last week.
Get 'em while they're hot (or cool, depending on how you set the multiplier.)