2) The Barter Variant. Basically you pick whatever armor you want to be proficient with at 1st level. For editions which focus more on category types than specific armors, pick the highest protection of armor you want to be proficient with. You still cannot use shields. Okay. Note how many points of protection that armor grants. Every odd level, beginning at level 1, you sacrifice one of the spells you would learn at that level and one of the slots you would use to cast it. So no first tier spell at level 1, no second tier spell at level 3, so on. You basically get access to every spell tier later, always know one spell less than you would normally, and always have one less slot to cast spells of that level. This continues for a number of odd levels equal to the armor bonus you chose. So you could choose leather armor and hamper yourself only at levels 1 and 3, for 2 points of armor proficiency, or you could get greedy and go for full plate and basically be a weaker elf who levels slightly faster. Your call.
3) The Losing Throw Variant. You weaken your own magic in armor in a specific way where you basically become susceptible to other magic. All saves against magical effects, items, and spells suffer a penalty equal to your armor's bonus.
4) The Little John Variant. Magic Users can wield staffs. You may reduce your maximum damage output for your staff by 2 points to improve your AC by 1 point. You must be wielding the staff in both hands for this to work, so you still do not benefit from this AC bonus in a round where you cast a spell, unless you use the staff to cast this spell.
5) The Enthusiast Variant. For every magic item you possess, including your spellbook and things like ammunition and potions, you have 1 pt AC bonus.
6) The Obsessive Variant. You may not own any object worth 1g or more (or 1s if you're on that standard) unless it is magic, but you can use anything that is magic. This means you cannot own a dagger or a staff or some rope but you can own magic rope, a magic staff, a magic longbow, or magic shield, and you can use those and benefit from all their glory.
7) The Bonus Spell Variant. All Magic Users may consider themselves to have both mage armor and shield as prepared spells. Casting them at higher spell levels grants an additional point of protection for each spell level.
8) The Opposite Armor Variant. Magic Users can wear any armor but cannot use magic in it, except for one spell: dispel armor, which only works on armor you've slept in. Once you are out of armor or it has been dispelled you may cast spells like normal.
9) The Fearsome Intellect Variant. Choose either Intelligence or Charisma, apply that ability score bonus to the MU's AC, ignore normal benefits of that bonus in other areas.
10) The Magic Car Variant. You are a vessel for spirits from the beyond. Choose how many spirits from the beyond you grant purchase in your soul. Your AC improves by that amount. These spirits manifest as spells that cast themselves when you cast a spell. You do not get to choose what these Spirit Spells are and the DM may swap out Spirit Spells when you become capable of casting a new tier of spells (however only a tier 2 spell or higher triggers the casting of a tier 2 Spirit Spell). You cannot control these spells to cast them on your own, they are not in your spellbook and you can't memorize them. You cannot control when the Spirit Spells are cast. Any time your MU casts a spell, the DM can pop off one of their own, targeting anyone and anything to any end the DM chooses, including targeting the MU. Common Spirit Spells are dispel magic (countering the MU's casting) and the LOTFP Summon spell.