If you're wanting to pick-up a USB3-enabled drive enclosure like the SilverStone TS07 or RVS02 (or any other USB 3.0 peripherals), but don't have any USB 3.0 ports on your system, the SilverStone EC03 can provide two USB 3.0 ports from a PCI Express x1 slot.
SilverStone's EC03 expansion card simply requires a PCI Express x1 2.0 slot and then it offers up an internal USB 3.0 connector with a front-panel 3.5-inch I/O bay that has two standard USB 3.0 ports. Of course, the EC03 adapter is backwards compatible with USB 2.0 and USB 1.1 devices as well. For necessary +5V power there is a 4-pin molex connector that can be fed from your power supply.
The SilverStone EC03 utilizes the NEC uPD720200 ASIC as its USB 3.0 controller. Unlike the recently reviewed SilverStone drive enclosures, the EC03 does not advertise any Linux support but only Microsoft Windows XP, Windows Vista, and Windows 7. Fortunately, however, this NEC controller is supported under Linux and the SilverStone EC03 had no problems functioning under Linux on modern distributions.