Updated version of design by gnabeyama: http://www.thingiverse.com/thing:136359
This version uses that one's lid, so you'll need to download:
"usb_case_top_repaired.stl", (I've added a copy on the Thing Files page as of 3/1/2015)

Customized this to fit one of the newer 6-pin USB UART 2102 Adapters floating around ebay for a mere .45 cents.

Changes include:

• raised walls to accommodate higher pin-headers.
• moveable board-retainer that prevents the chip from receding into the case when USB port is plugged in.
• & a cheater's window on the bottom so you can see which pins are labelled which without the need to remove the case.

5/7/14 - Update:.

Uploaded an STL version per franic's request.
Uploaded v2 "customuart_with_window-a-v2",Thing and .STL

v2 revision notes:
*longer window (so you don't mix up voltage)
*improved visibility (window view-angle)

1/31/15 - Update:.
Uploaded "custom_uart_openwindow-v3.stl" an open-window reference version intended for those who can't make the window adjustments or get this to print with a window, also tweaked the design slightly..

v3 revision notes:
*fully open window (non-adjustable .stl)
*more efficient print (quicker to finish, less filament)

v3.1 - minor fixes to bridge over the usb port.

This was my first design here. with literally less than 24-hours of 3d printing under the belt.. (nonstop, of course!)

Just slide the window piece till it lines up with your pin-labels. Remember to keep the window away from the solder-points.

Same procedure for the retaining-peg for the board, simply slide it to match your boards clearance.