I've seen three so far:
Belkin High Speed Express Dock
Targus ExpressCard Notebook Docking station
and, VillageTronic has announced the ViDock Gfx which is due to ship in the first quarter of 2008. It is claims to be the most capable of the expresscard video docks, with two independent video outputs. (DVI+VGA, or 2xDVI-I/VGA in the higher end model), however, it only offers video.
The Targus and Belkin offer USB, Ethernet (a SLOW ethernet port), audio, and one video output.