There are a handful of Thunderbolt enabled drives out there, but they are usually double-disk affairs (such as the Western Digital) or SSD (and very expensive SSDs at that). Nothing is enclosure only
Seagate offer an a Thunderbolt adapter for their external drives (GoFlex desktop and GoFlex portable), but again these are rather expensive (circa £150 and £100 respectively, just for the adapters).
I feel like i heard something from OWC about possible thunderbolt stuff later this year. There is def. something odd about this connectivity, licensing, etc, because so far we only have G Tech, Promise, and Lacie options with disks filled