Seagate has released their new series of external hard drives, the GoFlex Desk line, with 1, 2, 3 and 4tb varieties available.
The 4tb drive is selling for $250, and has several different options for connectivity, including USB2, USB3, and Firewire. Thunderbolt will be offered as another option soon.
Don't think I'd want the pre-installed backup software on the drive though.
Story and Seagate press release here at Endgaget: http://www.engadget.com/2011/09/07/seagate-plays-the-4tb-card-with-its-goflex-desk-external-hard-dr/