Best RAM for Core 2 Duos (Notebook)

The core 2 duo (mobil) has a 667 front sidee bus, and can utilize the DDR2-667 bandwidth.
In my tests, if you get low latency DDR2-533 or the regular DDR2-667 they are about hte same.
It really depends on how you utilize the RAM. If you are doing large transfers all the time compared to alot of ever changing smaller size transfers, this will change the "perfect" memory choice.

Ultimately, what Intel did to compensate for the memory controller being off-chip was to increase the cache size to 4 MB. Either one you choose will be fine, and right now, the fastest notebook RAM you can get is the 667 MHz.