A dagger that I dug up that allowed me to see the invisible "grey claw" creatures that were slowly invading our plane of existence. Spent 3 years with it soul bound to my hand, getting myself mauled by both the creatures as well as those who wanted me to defeat them (being drawn and quartered by two dragons was especially interesting). Ended up having to fight the leader Greyclaw that had 500 HP, I had 15. It swung for 30, I swung for 2. But I managed to hit it with 9 out of 9 banishment spells while it chased me. It died, my dagger exploded in my hand (taking my hand with it) and in its place was a madman cackling and saying, "Thank you!" to me over and over again as he ran off into the woods.
It was at this juncture that my character swore off of magic from that point on and has never possessed a magical item for the last 20 years.