Inspired by a "useless items" list: Torch of Darkvision (Plurk Paste)
Unlike the thing that inspired it, though, this actually would be useful in a few ways.
Valuable for explorers in areas frequented by species prone to attacking people carrying light sources!
(Or just needing to get past that Shrieker patch without alerting every predator in the entire cavern system...)
Unrelated to the proposed item above, I notice that "Stone of Gravity Detection" seems to be a popular useless/joke item. 
(This, of course, being a stone that when you release it in front of you will move toward any strong nearby gravity source. )
)
(In other words, a rock with Nystul's Magic Aura cast on it XD)