eSATA-only HDD enclosures
It is difficult to find hard drive enclosures that only have an eSATA interface (no USB and no Firewire). But eSATA-only enclosures can have certain advantages in compatibility and performance. Because eSATA uses the hard drive's native SATA communication protocol, there is no need for the enclosure to contain a bridge board that translates the hard drive's native signal to the USB or Firewire protocol. For some use scenarios, bridge boards introduce unnecessary complexity that can result in reduced performance or impaired compatibility (e.g. bridge board firmware bugs and incompatibility with power management features of the user's operating system).
Here are two eSATA-only single hard drive enclosures I was able to find: