Acording to Anandtech, you should go with Crucial Balistic PC3200 or OCZ 3500EB or 3700EB. To quote them:
"The overall best Athlon 64 performance that we have found was with Crucial Ballistix PC3200, and our alternative, OCZ 3700EB/3500EB. These two memories perform just as well on Intel DDR systems, but they stand alone in performing the same on the pickier Athlon 64 Socket 939 boards.
When Corsair 3200XL roared on the scene in May with a return of 2-2-2 timings to DDR400, we had no idea it was just the start of DDR400 2-2-2 from all the major memory makers. As you saw in our roundup of the new 2-2-2 memories, all of the new DDR400 2-2-2 performed well on the Intel test bed and all, but one, used Samsung memory chips. The exception was Crucial Ballistix, which used Micron memory chips and earned our Gold Editors Choice for best performance. Ballistix was also the only 2-2-2 memory tested in the roundup that performed just as well on Athlon 64 as it did on Intel, so it is a great match to the MSI K8N Neo2.
Crucial Ballistix also extends performance all the way to DDR500, with our test memory achieving the fastest timings that we have tested so far at DDR500. This will give you incredible headroom when you select this memory for your system. "
