I just spent the last several hours looking through tvtropes to see if there was a mention of something that gives you more than three wishes, because I didn't think three wishes was enough.
I suppose I could just say d&d, because one probably exists. There's definitely a ring of unlimited wishes in some sourcebook or other.
Anyway, besides that (wish-granting items in general are kind of a cop-out) there are of course a lot of other tempting choices:
- The Pick Of Destiny (already mentioned in the thread, I don't even know if it has actual powers besides being awesome, but you know that we'll be rocking cause it's fuckin insane.)
- The briefcase from Pulp Fiction - also saw this in the thread and though "Damn. I want that." despite the lack of actual world-changing power.
- An ACU from Supreme Commander. In Supreme Commander, the crazy-fast build times of your typical rts are actually justified in-universe because of the advanced nanotech they have, so this thing is a 20-metre-tall giant robot that also happens to be able to build an army in a couple of hours.
- The recipe for the Grand Panacea, from Baccano!, because immortality.
- The magic ticket from Last Action Hero.
Then of course, there's about an infinite number of spaceships, time machines, and time-travelling spaceships that I could mention, out of which I will grudgingly have to be unoriginal and say "TARDIS", because on top of being a time machine and a spaceship, it's crazy-huge as well, and I'm not sure if anything can top that combo, o matter how badass an Overlord Dropship might be.