Seagates 'Cuda IV 40GB/platter was the first one. I read rumors that a Cuda V is soon t come, but no details.
I personally think the WD80JB is THE drive to get. If it's available anytime soon.
Increasing platter density isn't that important anymore .. I think. The jump in performance from 20 to 40GB/ platter wasn't much, considering that it was an increase of 100%!
I'd prefer larger caches. And if you look at the recent SDRAM prices, it would cost them nearly nothing to add 8 and 16MB caches.
Serial ATA, fluid bearings, higher RPMs and internal raid 0 would be great as well.