Western Digital has a new first under their belts. This is the first 2 terabyte drive. It was not that long ago when 500 Gigabyte was thought amazing and now we have four times that on a single drive.
But sheer size is not the only thing that you get with the new WD20WEAD also called the Caviar Green 2.0TB. WD has acked in 32MB of Cache and some power management code to balance spindle speed with the cache to maintain transfer rates.
They won't be cheap but if you need the storage you can't get bigger than these right now.
Pricing at Mwave