First magic item I ever acquired in D&D was a dancing sword!
The party (of 13!) was fighting a tough fighter, when all of a sudden his sword leapt up and started fighting us by itself, while he drew another weapon. Yikes!
Having only 1hp I'd pretty much kept out of the fighting and stuck to doing thievey things; the fighter was eventually killed (he was back holding the sword at that time) and the rest of the party went into the room attracted by the glittering gold.
So I asked the DM secretly whether anyone was looking at me or the body, and they weren't, so I asked whether I could replace his magic longsword with my ordinary longsword, and I could... and the rest was history (being about 1976 it was probably ancient history!)
Cheers