what is the best heatsink for an anthlon xp (1800+)?
mine (global win fop38) is on the recommended list of AMD.com

Its a price question. The very best heatsink is an slk-900 with a zalmon 92mm 119cfm fan on it hooked to a fan controller so you can turn down the speed and make it quiet while still getting awesome cooling.

Next best is an slk-800 with a thermaltake smart fan on it. Much cheaper, but still not cheap.

Only a little down from that in cooling is an sk-7 with a medium or low rpm 80mm fan, for $25 total at

http://www.svcompucycle.com/

The fop38 is a good cooler, its just loud. If you don't mind its fan noise I don't know why you would change since it certainly gives adequate cooling. But if you do want a quieter cooler make sure you get a copper sink and a low rpm or a manually adjustable rpm 80mm fan (the slk900/92mm fan is extreme) since that will get you the lowest noise / cooling ratio.

This one is nice I wish i could find a place that sells them.

http://www.tomshardware.com/cpu/20030404/amd_cooler-05.html