SmallHD, best known for their HDMI monitors, developed an HDMI port protector for the 5D Mark II, which it sells for $50. When the 5D Mark III came out, Canon had slightly changed the body. Accordingly, the SmallHD port protector for the 5D Mark II would not fit.
SmallHD went back to the drawing board and made an even better port protector for the 5D Mark III, which includes a HDMI and a USB port protector. Now, the port protector benefits both HDSLR shooters and tethered shooters. At $50 for the port protector (through Kickstarter), this looks like a great accessory if you are a heavy user of either the HDMI or USB port on the 5D Mark III.
The Kickstarter campaign only has 12 days left and they are a little short of the funding at the time of this post ($18,504 out of a $22,000 goal). If the port protector gets made, it will be $60 at retail. You can find more about the project here on Kickstarter.
(Thanks Pieter for the tip.)