WoWDB

This item is super fun.  It shoots you far, and you can throw the coin anywhere (targetting retacle) to propell yourself any direction.  There is only a 1 second cooldown (right now) so you can basically use it endlessly.  The only limitation is that you must be outdoors.  You have to pickpocket some coins for it to work, but that part is easy.

Also IT WORKS WHILE MOUNTED!!!

Note that your amount of coins resets when you teleport (hearth, mage portal, use a boat/zeppelin, etc) and that you can only use this item in a zone where you can fly. This means you cannot use it in Pandaria until 90, for example.

Obtained by talking to Orsur while wearing the guise of Reislek's Ghost. This is a further Mistborn reference as Orsur is actually OreSeur from the Mistborn series, and you must tell "Orsur" 'I am your master.' for him to give you the bag. Kelsier (the ghost) is Orsur's master.

In Warlords of Draenor, this item will be added to the new Toy Box feature and no longer take up a bag slot.  You will be able to "use" the item straight from the Toy Box interface. 

The Toy Box will be account-wide and therefore so will this item.  However, since it requires pickpocketed coins in order to work, it stands to reason that only your rogue alts will be able to enjoy this.

You can probably also use many other different forms of invisibility detection as well, then. For example,  Invisibility Potion says it has 1000 Invisbility Detection (same as Revealer) - probably so that you could see yourself while invisible.