Ring of Incredible Strength - rare - While you wear the rare version of this ring, your Strength score gets set to 21, and you can choose to use a weapon with the two handed property with one hand (only affects one weapon at a time) or to use a weapon with the heavy property as if it didn't have that property.
So sword and board with a Greatsword while getting the +2 from dueling.
Flaming Beserker Greataxe - rare - You gain a +1 bonus to attack and damage rolls made with this magic weapon.
While you are holding this weapon, you can use an action to speak the command word to cause the weapon to burst into flames for 1 minute. During this period, you gain a +1 bonus to attack and damage rolls made with weapon. Additionally, when you hit a creature with the flaming weapon, the target takes an additional 1d12 fire damage.
The flame does not damage or otherwise harm you. The flame vanishes after 1 minute or when the weapon is removed from your hand. Once you use the weapon's property, you cannot use it again until the next dawn.
Fullmetal Cloak Plate armor - rare - This armor has two forms it can switch between using a bonus action. Due to its animated design, if you have proficiency in light armor, you are also treated as having proficiency in heavy armor while wearing this cloak, and you do not have disadvantage on stealth checks.
Cloak mode: The armor wraps loosely around your body, like a cloak made of metal plates. It lashes out at attacks that would hit you. When you would be attacked by a ranged attack, you may use a reaction to increase your AC against the attack by 4. The cloak can also slow your descent, allowing you to use a reaction to reduce fall damage by 20.
Carapace mode: The armor wraps tightly around you, turning into an armored carapace. You are given an additional +1 to AC. Your land speed increases by 10 feet, and your jump height and distance are doubled.
Other options for rare magic items-
Regular +2 weapon
Regular +1 Armor
Regular +2 Shield <<<<<really OP
Amulet of Health - sets Con to 19
Belt of Hill Giant Str - sets Str to 21
Ring of Protection - +1 to AC and all saves