Pretty self-explanatory; I began wondering this when I misread the description of Mithral Shirt and thought it could be worn on the body slot in addition to existing armor to grant additional AC bonuses, but I guess this isn't the case. Does anyone know of other items that can grant AC instead of/in addition to armor and shields?
Note that this doesn't necessarily need to be a body slot item; I just mean anything other than armor and shields that can up my AC.
Yes. There are numerous types of AC Bonuses that come from a wide assortment of items and stack together. AC Bonuses of different types all stack together (and Dodge Bonuses stack even with each other).
A common set of AC Bonus types that one might have together would be Armor, Shield, Deflection, and Natural Armor. Each of these can be gained either through mundane means (wearing armor, wielding a shield, having naturally tough skin from a racial trait) or from magical equipment (Bracers of Armor, Animated Shield, Ring of Protection, Amulet of Natural Armor). Wizards, for instance, can gain all of these things without using the method of doing so that hinders them (though it is definitively more expensive).
These are super-rare for obvious reasons: usually bonuses of the same type do not stack, and you typically cannot equip two items in the same slot. The only exceptions to this that I am aware of are the dastana and chahar-aina from Oriental Adventures as updated to 3.5 by Dragon vol. 318, which explicitly stack with the armor you’re already wearing (the enhancement bonuses to each’s armor bonus to AC don’t stack, but the base armor bonus to AC and special armor properties do). They are separate, mundane items you wear in addition to your armor in the same slot, and can be enhanced separately. Usually just a bit cheap since it’s much cheaper to get magic enhancements spread around several items than it is to get one item with all the enhancements. So check with your DM to see if they’re allowed.
The only other thing you can do is try to add wondrous-item bonuses to AC (e.g. the enhancement bonus of a ring of protection, the natural armor bonus of an amulet of natural armor) to your armor; you will almost certainly have to pay the 50% surcharge for putting these effects on an unusual slot, if it’s allowed at all.
