Amulet of flying
The amulet of flying is a new piece of jewelry introduced in SLASH'EM and UnNethack. It grants the flying intrinsic, which is similar to levitation but far more useful. In UnNetHack, this amulet is one of the rewards for solving Sokoban.
Flight is a property possessed by some monsters, which is superficially similar to levitation but has generally more controlled effects, covered on the page about flying. Of its effects, the only one which is negative is being unable to reach items in pits. This is of course easily solved by taking off the amulet on the rare occasions that a valuable item falls into one. Note however that you can descend in to holes with the > command ("You jump through the trap door."). You don't need to remove it then.
Flight is superior to levitation in almost all manners. Basically, it allows the player to not need to worry about terrain much at all, since it allows one to usefully cross and interact with any sort of terrain. In addition, the amulet cannot be destroyed by an electric eel or removed by an incubus, making flight over water considerably safer than levitation over water with a ring. The only possible downside is not being able to use Newton's 3rd law for a quick escape in some situations.
This is a valuable item for any player to have on hand, as it removes the need for fountains when diluting potions, and is more convenient than water walking boots. The multitude of other positive effects means that for a careful player who already has drain resistance, this amulet is well worth considering as an amulet in an ascension kit. In particular, it removes the need to switch rings to levitate, which is quite useful in SLASH'EM, given that free action is somewhat more essential. Drain resistance should be given priority, however, although a careful player may find it feasible to quickly switch amulets or wield an artifact that provides the intrinsic. Some players may still prefer life saving, but for those who don't, an amulet of flying may be just the thing.