You’ve seen it before. The +1 Magic Sword. The +2 Plate mail, scattered across modules in place of actually interesting loot. It’s boring, and not very fun. Here are some suggestions for in world effects that can replace them. These stack, meaning that a +2 sword will have the +1 and the +2 bonus.
+1: Made of unusually good quality. Doesn’t break where other weapons would, resistant to spells like “heat metal” etc.
+2: Environmental effect. Tied to the biome in which you’ve found it, for example in a volcanic biome a spear may have a 1 in 6 chance of flashing with heat when striking an enemy, volcanic armour may protect the wearer in cold biomes etc.
+3: Legendary. Absorbs elements and turns them to their own power. If a fireball hits a +3 shield, it becomes fire resistant. If a fireball hits a +3 sword, it gains the ability to shoot small bursts of fire. Usually a legendary tool can have at most three qualities, and the bearer has to survive for this sort of “learning” to take effect.
+4: Godlike. Has a will and mind of its own, Charisma save to resist getting dominated. Weapons automatically kill weaker enemies (<2HD) on contact, armour has a damage threshold (roll 2d6 to determine).