I am curious about what unusual methods of healing you have found useful.

Note that I consider the standard methods of healing to be:
Having one of your characters cast a divine healing spell (Cure Wounds/Heal)
Having one of your characters drink a healing potion

Two alternative methods of healing I have used in Baldur's Gate 2 (both available early) are as follows:
1. Cast Call Woodland Beings, have the summon cast Mass Cure
2. Use Vhailor's helm, then let the clone use a Rod of Ressurection.

I can't remember, charmed characters in BG2 can use their specials abilities?

And from the first game, using charm spells to charmed back a charmed companion (Though this was suggested by the same game)

There's a bunch of ways:

at an inn -- (Heal on Rest)
at a temple
Gloves of Healing
Staff of Healing
Constitution 20
Polymorph into a troll

There may be more.

I rarely ever command my party members to use any healing spells or abilities after they obtained certain magical rings.

Chug a potion of absorbtion and cast lighting bolt into a wall in a narrow hallway. This worked in BG1, not sure about BG2 though

Actually, any method of getting your resistances over 100% will work. For example, stack Armor of Faith until your resistances are over 100%, then have someone else attack that character. Alternatively, use the Cloak of Sewers to turn into a rat, then cast Armor of Faith with a sequencer, and then have someone attack that character.

From what I hear, the first Baldur's Gate has a weapon called the Vampiric Blade that reverse drains whoever it hits. Give it to a character with 20 Constitution and that character can be a rather effective healer. (Why doesn't Baldur's Gate 2 have useful cursed items? Maybe on my next attempt, I should cheat that weapon in.)

In the Enhanced Editions, cast Protection from Fire on a Dragon Disciple, then cast fireballs at her. They will heal her but will still disrupt her spells.

True, but lightning is the most efficient way because lighting bolt bounces off walls meaning one character can hit repeatedly. Also, the potion of absorbtion gives 100% electrical resistance as opposed to 50% fire, cold, whatever resistance other potions have so getting above the 100% threshold is just much easier,

True! Didn't remember my fight with the phoenix warriors, almost a full town got killed meanwhile my PC got a "refreshing" breeze.

My favorite involve free abilities so to speak.

In Baldur's Gate 1, my favorites are the free Cure Light Wounds spells you get if you have a positive reputation for your main character as you progress, since they have an instant casting time much like Lay On Hands and are basically free. The others would be using Lay On Hands from a Paladin or equipping Buckley's Buckler on a character with 19 Constitution for health regeneration giving them 20 Constitution for as long as they wield it..

This is me. I hear the fixed it in EE, but man, it saved my life a hundred times.

I actually don't like the fact that EE and mods "fix" things like these, especially since the mods that do so don't let you pick and choose, so you can't just get legitimate bug fixes while avoiding the game balance affecting "fixes". (I note, in particular, that such a fix makes Armor of Faith useless at lower levels.)

When I get around to playing Icewind Dale: Enhanced Edition, I am thinking of maybe undoing any fix that bothers me. In particular, the "fix" that prevents you from using multiple Projected Images will likely go, mainly because it prevents you from summoning another immediately after the first one gets killed.

(Also, I may change the behavior of Vampiric Touch. The fact that you can't recast it for more healing really bothers me. Then again, I haven't seen a single (A)D&D game that correctly implements that spell.)

I must say, I didn't even realize it was a bug. I thought it was intentional in the way the elements worked in the world.

It made complete sense to me. Almost like you become an elemental. If you have 120% resistance to lightning, then you feed on it. So dish it out, suck it in, and feel the power.

I just tested the Procection from Fire/Dragon Disciple combo in IWD: EE (probably works with Baldur's Gate 2: EE as well), and fire actually did heal the Dragon Disciple. Just cast Incindiary Cloud and have the 127% fire resistant Dragon Disciple walk around in the area and she will be healed each round. Even better, enemies that try to attack her will take damage if not fire immune. Unfortunately, the fire "damage" still interrupts spells.

Tested with IWD: EE version 1.4

It makes absolutely no sense whatsoever. A resistance is just that, a resistance. It does not mean that above 100% you feed on that resistance, that's preposterous. Hypothetically, if you have a tough skin that gives you complete resistance to piercing arrows, that does not mean that improving your skin makes arrow *heal* you. It's nonsense.