The Eye of the Aethiopica

The Eye of the Aethiopica is the wizard quest artifact. It is neutral for wishing purposes; if you are a wizard, it will adjust its alignment to your starting alignment.

Its base item type is amulet of ESP, so wearing it provides extrinsic telepathy. You can also abuse the naming artifacts exploit to determine whether an unidentified amulet is ESP or not.

You can invoke the Eye to branchport. In other words, you can immediately teleport to another branch of the dungeon that you have visited. You arrive on the deepest level of that branch that you have visited. Attempting to branchport to the branch you are currently in gives the message "You feel very disoriented for a moment." and has no effect. Adjacent following monsters will follow you through the gate into the new branch; this is a common method to transport many wraiths from the Valley of the Dead so they are more likely to leave a corpse. The branchport ability of the Eye makes Sokoban an ideal stash location. A typical branchport menu might look like:

                                              Open a portal to which dungeon?
            ----------                        a - The Dungeons of Doom
            |........-####      ------------- b - Gehennom
            |........|   #######-...........| c - The Gnomish Mines
            ----------          |..@........| d - The Quest
                                --------+---- e - Sokoban
                                        #     f - Fort Ludios
                                        #     (end)

When carried, The Eye provides half spell damage, magic resistance, and fast power regeneration. With fast power regeneration, you restore about one power per turn -- this is far quicker than you would otherwise.

In the opinion of many experts (such as Rast and Eidolos), the Eye of the Aethiopica is not only the best artifact in NetHack, but also the best item.