I was personally looking at the Seagate Momentus class 160GB drives (ST9160821A) because they were the first ones out there, but there are competitors out there now. Just be careful to get Parallel-ATA if you want it to work in the empeg with no additional interfaces / adapters. Froogle is showing them averaging between $220 -> $250 each. (newegg has them for $225 each...)

You should be able to run two in an empeg with no additional tampering. Although you will likely have to build them manually and probably need to run hijack as well.

They have come down a lot in price, but I cannot justify the upgrade right now... (Four players x two drivers per player...)