Let's have some fun with inventing an artifact.
Armor of Achilles - Forged by Hephaestus himself, the armor of Achilles is leaps and bound better than any moral armor. This adamantine armor provides a +10 armor class and a +5 enchantment bonus. The armor is so amazing that the wearer can nullify one melee attack or magical effect per round. What would normall be a hit is instead reduced to a miss. Any magic effect about to affect the wearer, or already affecting the wearer, is also nullified.
Bow of Ulysses - This bow requires an 18 strength to use. The bow is +5 to hit and damage, and adjusts its pull to the strength of the user. In addition, once per day, the bow can fire any arrow as an Arrow of Slaying.
The Goose that Laid the Golden Egg - This goose lays one golden egg per day. Each egg is worth 10 gp. If eaten, the goose feeds 4-6 people and, being dead, lays no more eggs.