The Orb of Aldur from the Belgariad. A sentient (but not very intelligent) magical artifact with virtually limitless power. The full extent of its power isn't explored in the books, but it's the only thing in the world that can drive away or seriously injure demons (and demons in the Belgariad are matched only by gods), can effortlessly hold off the dark god Torak, and it once split a continent in half and nearly destroyed the world. It's even implied that it has enough power to alter the stars themselves. In a conversation in the Malloreon, Garion reveals that if he just thinks about doing something, the Orb tells him exactly how he could do it, and will sometimes straight up attempt it on the spot. In that conversation, he gives the example of writing a name in the stars in the night sky, and the Orb of course almost goes ahead and does it. Aside from the "literal omnipotence" and "infinite wishes" items from fiction, I can't think of anything that matches the Orb.
