One of the promises of Thunderbolt was the ability to use PCIe cards externally, meaning users of any Thunderbolt-equipped Mac could use such cards. In the past, of course, this type of flexibility and and expandability was reserved for users of the the Mac Pro (and the PowerMacs before).

The Sonnet Technologies Echo Express SE Thunderbolt Expansion Chassis is the fulfillment of that promise. The aluminum box talks to any modern Mac over Thunderbolt, but the magic is inside, where it can house a single half-length (up to 6.6"), full-height, single-width, x8(1), PCIe 2.0 card.

If you need something a little cheaper, the Helios PCIe Expansion Chassis from OWC is a $349 chassis that can accommodate half-length, single-width PCIe cards compatible with Thunderbolt technology. And it's dressed in black, which is hard to argue with.

Both boxes include a second Thunderbolt port for pass-through, and both require external power, so you're gonna need an outlet to run either one of them.