One of these;

http://www.belkin.com/au/F4U055/p/P-F4U055/

Adds a plethora of ports to a Thunderbolt-enabled Mac computer.

Primarily useful to get Gigabit ethernet, Firewire 800 and a couple of extra USB 3 ports on a Macbook Air.

Includes a 50cm Kanex thunderbolt cable.

Includes all original boxing & packaging.

$200 Incl. Non-RD Courier