There is a quest in Blade's Edge Mountains called "The Smallest Creatures". [Edit] Sorry Alliance, Horde only.
[Only registered and activated users can see links. ]
When you take control of a Marmont, you gain a buff that allows you to hide into the background. However, the Marmont is considered a pet, and thus you can dismiss it. The trick is that after you dismiss your Marmont, you still maintain the 5 minute invisibility buff.
For the duration, you are completely INVISIBLE and UNTARGETABLE. During this time, you can go on a pure ganking spree. Hostile players are completely unable to attack you. And NPCs will also ignore your attacks, even in towns and cities. This includes guards. The only way that the effect is broken is if you attack a NPC directly.
[Edit] I found a much much more useful application for this than simply ganking alliance. This buff is not removed by zoning. Quests that require you to loot an object in a instance, such as [Only registered and activated users can see links. ], are now easily soloable. Simply set you're hearth near an instance, or have a summoning group ready. Next, receive the buff, hearth or summon, and enter the instance. While in the instance, you can gather herbs and mining nodes freely. Also, you can run to any interactive object without fear of mobs. Opening chests, collecting nodes, collecting quest items, etc, DO NOT break invisibility. So as long as you do not attack a NPC, you have free rein in any instance.
Enjoy your 5 minutes of bliss. And yes, you can do this as many times as you want.
PS. Although this is a use of in-game mechanics and not technically a cheat, it is outside the bounds of intended implementation, so punitive measures from a GM if you are caught are not known at this time.