Get the AKE USB 2.0 card based on an NEC chip. You will need to power the card or external peripherals if they draw too much energy but most usb flash drives work without additional power.
This one sits flush and firmly enough so that you can plug and unplug devices without dislodging it. Expect to pay about £3-£5 shipped from China. It is my recommendation and the one I use. Others may suggest something better.