The Register received word that Seagate is planning to release a 3TB HDD this year. The disk will be part of the Constellation ES series and will feature a 6Gbps SAS interface.
The Constellation ES is a replacement for the Barracuda ES and is, Seagate says, an enterprise class drive, currently maxing out at 2TB, and spinning at 7,200rpm. There is a 2.5-inch version which tops out at 500GB capacity.
Our understanding is that a 1TB version of that product will also arrive around the mid-year point, and be the world's highest-capacity 2.5-inch drive, exceeding products offered by Toshiba and Western Digital.