It seems that it’d be Western Digital WD4000YR. Check this out : 400 GB capacity, 16MB buffer, uses WD’s Raptor technology heavily, beats pretty much all other SATA hard disk in various benchmark, and so on.
A bit of history; I bought 2 WD Caviar SE 120 GB, the ones with the (then) phenomenal 8 MB buffer, making it the (then) fastest ATA hard disk. Unfortunately, they seems to be not very reliable, with both already dead.
Reading the review above, it seems that WD has fixed this issue.
It seems to be THE hard disk to buy if you’re a power user.
Do you agree ? Let me know.