If you just want RAM then get any kind of decent name value RAM. Keep an eye on the Hot Deals forum and you can find a gig in the $120-140 range. I have some Mushkin Value ram that was $130, and recently there was some OCZ value RAM for $120.
If you're talking about pushing the FSB up, then you're talking about something like Crucial Ballistix or OCZ EB (comes PC3200EB/PC3500EB/PC3700EB). Those will run much better timings and higher FSBs, but are about double the cost. They use the Micron chips that seem to work best with the A64 platform.
If all you want is regular RAM, stick with the Value RAM of normal well known brands like Mushkin, Kingston, OCZ, Crucial, Corsair, etc... There aren't any specific incompatibilites that I am aware of with the A64. Keep in mind that the memory controller is on the CPU, so the board doesn't matter as much for RAM compatibility as when the memory controller is on the northbridge as in the P4/AXP platforms.