Update:
I found a picture in an article of one of the above:
http://www.dreamwarecomputers.com/index.php?option=com_content&view=article&id=5531%3Asilverstone-ec01-usb-30-internal-card&catid=1%3Aaccessories&Itemid=2&limitstart=2
I couldn't figure out the difference between these two cards from Silverstone. The advantage they have over the one I found is they offer USB3. The disadvantage is they take up a PCIe slot.
If you have a spare PCIe slot then I highly recommend one of these Silverstone PCIe cards.
*WARNING:
Although you can use ANY PCIe slot (x1, x4, x8 or x16) be aware that some motherboards will HALVE the bandwidth on the main PCIe (i.e. x16 to x8). Most people don't have a graphics card fast enough to max out a PCIe v2 x8 slot (I think you need a GTX570 to do that) but I thought I'd bring it up.
If in doubt, read your motherboard manual. If still in doubt:
1. Use any benchmark utility (3DMark series from Futuremark) that stresses the graphics and get a SCORE before the addon card is inserted
2. Get the addon card up and working then obtain a new SCORE with the exact same benchmark settings
(the above also applies if you're getting a PCIe sound card and question if it will impact your system. Even if you KNOW your main graphics slot will go from x16 to x8 this is the test to see if it MATTERS in practice.)