These guys come in various sizes and speeds: 5400rpm drives: 320GB, 500GB, 750GB, and 1TB. 7200rpm drives: 500GB and 750GB. And the 1TB is only $230.
They connect via the usual suspects: USB 2.0, USB 3.0, Firewire 400/800 and eSATA. You can even use this on a Mac with the drive NTFS-formatted.
Price: starting at $99
(Please note prices are subject to change and the listed price is correct to the best of our knowledge at the time of posting)