Silverstone has released the hard drive pad SD01, which is stackable and compatible with SATA or SAS hard drives at up to 6Gbps speed.
The hard drive pad, also known as the Stackable Drive series SD01, supports both 2.5" and 3.5" SATA/SAS hard drives. The maximum data transfer speed via either interface (SAS uses SAS dual-lane interface, SATA uses eSATA interface) is 6Gbps. The SD01 can support drives of greater than 2TB capacity and runs on a 12V power cable (4-pin molex cable is provided). Silverstone SD01 comes in black, weighs about 180g and measures at 195 x 121.5 x 31.5mm. It is currently retailing in Amazon at US$36.50 (S$44).
See more specifications at the Silverstone website.