Korean AL Tech offers a multimedia HDD enclosure with Ethernet port.

When we reviewed the TVisto, we mentioned that a network connection is an essential feature for AV Hard-drive enclosure. Else you always have to carry the box from the TV to the PC and vice versa.
The MediaGate MG-35 can be equipped with a 3.5 inch HDD. It plays MPEG 1, 2, 4 (MPG, MPEG, AVI, M2V, DAT, VOB, etc) DivX 3.11 higher and XviD (Except GMC, Qpel option applied) videos. MP3, OGG Vorbis and WMA audio files. Besides the Ethernet port the HDD enclosure also has of course an USB 2.0 port.

The Mediagate MG-35 is selling for $199.00 in the US.
The Mediagate MG-35 measures 57 x 150 x 185mm.
More details on the AL Tech product page (Thanks Joey).