Matrox DS1
Matrox DS1 gives you the most from your Thunderbolt port by letting you add a large display, a full size keyboard, a mouse, a wired network, and many other peripherals using a single cable. In an instant, you enjoy all the productivity benefits of a desktop computer.
When I eventually upgrade to a Thunderbolt MacBook Pro, I would be interested in a more professional-level dock. It seems that nobody makes one right now. The $249 (plus $50 cable?) DS1 doesn’t offer dual-link DVI or DisplayPort, so it’s limited to smaller displays, and it has only one USB 3 port and two regular ones. The $300 Belkin dock also has limitations. A dock that supported a full-size display, that had enough fully powered USB ports that I didn’t need any hubs, maybe even FireWire or eSATA—that would be interesting.
Update (2012-06-06): AnandTech covers the Matrox and Belkin docks.
The DS1 apparently has only one Thunberbolt port. Apparently, Matrox think they are special and that you will obviously want their device at the end of the chain, because who would not want to unmount all their USB devices in order to unplug the portable Thunderbolt hard drive that they had to plug in the middle?