Athlon 64 Optimizations
Its been hard to find code optimized for the Athlon 64. Here were some threads I found on the topic as folks struggle to do this:
* mersenneforum.org - Creative ways to achieve Athlon 64 / Opteron optimization
* "AMD64 Optimized":http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_9485_9488^9563^9598,00.html. The small list of folks doing 64-bit optimizations. Biggest names are probably America's Army (a cool game) and Dr. DiVX encoding. Both of these require 64-bit Windows (in beta now).
* "AMD-64":http://www.x86-64.org/. A site sponsored by AMD for developers writing 64-bit applications.
* "PlanetAMD64":http://www.planetamd64.com/. Another enthusiast site with announcements
* "Mandrake":http://www.mandrakesoft.com/products/92/amd64, "NetBSD":http://www.netbsd.org/Ports/amd64/ and "FreeBSD":http://www.freebsd.org/platforms/amd64.html, "Suse":http://rootprompt.org/article.php3?article=6061, "Debian":http://lists.debian.org/debian-amd64/ ports to AMD64