Here's mine.

Regular mode:
1) Cera Sumat/Holy Avenger. This weapon makes a Paladin into a valuable asset. +5 weapon, check. Dispelling capabilities, check. Damage against evil opponents, check. Epic quest to acquire such, check.

2) Greatsword of the Soulless +5. Great for a Barbarian, Fighter or Ranger. Sure, it's only available at the very end of the game, but it's good for going into HoF mode.

3) Club of Disruption. This makes fights against undead, outsiders and elementals trivial in normal mode and easier in HoF mode.

4) Ice Spear +4. Acquired at the same time/place as #3, it's one of the first +4 weapons you get if complete the Battle Squares in Chapter 2.

5) Snow Leopard Charm. Good for heavy armor-wearing Paladins, Clerics or Fighters who don't already have a +1 Dexterity to AC.

6) Mithral Field Plate Armor +2. Sure, it's random loot at the end of the game, but if you manage to snag this, this is very useful for Barbarians as well as Fighters, Clerics or Paladins. Just make sure you have 14 or 15 Dexterity to reap the maximum benefit.

7) The Unstrung Harp. This instrument becomes useful later on, particularly in pitched battles or especially in HoF mode.

8) Everlast Arrow. An arrow that never runs out? Why not?! A shame they didn't make similar ammo for slings and crossbows.

9) Little Giant. Great for Fighters, Barbarians or Rangers who focus on melee combat.

10) Ring of Freedom of Movement. Once you get this, at least one party member should be able to walk through anything. Best for healers, followed by arcane spellcasters.

HoF mode:
1) Kegsplitter of Shaengarne Ford. This becomes highly valuable against kegs in the aforementioned region in Chapter 1 (which act more like M1 Abrams tanks minus the armaments) as well as golems in Chapter 4, which can be a hassle if not a health hazard. Don't know if said weapon works against the Ice or Crystal Golems in Chapter 2.

2) Scales of Balance. The BEST battleaxe in the game. Has versatility in itd special abilities to tailor more to the wielder.

3) Light of Cera Sumat. Simply put, Holy Avenger on steroids.

4) Blessed Flank of the Virgin. Very good for a weapon-and-shield character in need of Dexterity that also wears heavy armor with a +1 or +2 maximum Dexterity bonus, like a Cleric or Paladin.

5) Air Genasi Gail Armor. BEST armor for a Paladin, Cleric or Fighter missing a Dexterity bonus.

6) Phaen's Tattered Robes. Very good for reaching a minimum of 30 AC for a Sorcerer or Wizard for HoF mode, at least until you can purchase the Robes of Good/Neutral/Evil Archmagi.

7) Indomitable Bands. Takes a massive nip out of many enemy melee attacks.

8) Bands of the Master. Similar to above.

9) Raging Winds. HIGHLY invaluable. Nothing like summoning up to 6 berserkers who hit decently but most all act as powerful fodder so you can whittle down opponents without taking much (if any) damage. Makes a bard a must-have.

10) Shifter's Nimble Boots. It's like a Ring of Freedom of Movement for your character's feet!

What about you folks?

I'll probably contextualize the thread as useful items in IWD2, not necessarily the best. Also, I'll only stick to Normal. Here it goes;

Massive Halberd of Hate +4 - great weapon, guaranteed to be found in chapter 5, with 5 ApR, it's a serious roomsweeper.

Brilliant Short Sword +5 / Belib's Everlasting Torch - 2-handed weapons pre chapter 5 aren't that great, yes, there's Ice Spear +4 and the Sherincal greatsword can be useful against Auriliates in chapter 2 and barbarians in chapter 3. Nonetheless, dualwielding these 2 weapons with power attack +5 is a powerful replacement, at least until chapter 5.

Sad giant's cap - +4 buckler, with arcane spell failure 5%, 1 pip in armored arcana and expertise and your wizard can have very respectable AC.

Sash of the Black Raven - immunity to confusion in chapter 1? I'm game.

Houndstooth Collar - Immunity to fear/panic, useful to remove one vector of attack for cleric, afterwards can cast remove fear on the party.

Brazen Bands - +5 to AC, stacks with other armor types (generic), excellent item.

Golden Girdle - +3 to AC against a very common attack type (slashing), stacks.

Holdfast Arrow - Entangles enemies upon hitting them. Unlike other magical arrows with special effects, Holdfast arrow has no DC check, i.e., if you can hit your enemy, you have a guaranteed entaglement. The Lost Followers encounter and others are triviallized with this. OP.

Protection from Magic scroll - another OP item, there are only 3 in the game. Dispels all protective buffs and prevents them from being recast. Iyachtu Xvim, M'darfein and others drop dead instantly.

Shield ring / Shield amulet - short duration, but can be useful to buff AC in specific fights, i.e. in the fight against Chahopek, you can probably reach ~60 AC on normal with normal race (no deep gnome).

Every God Ring - +5 to Wisdom and there's no Owl's wisdom spell in the game, a no brainer.

Tymora's Loop - Difficult to get, +3 to luck, obviously very useful.

Throwing Hammer of Thunder +2 - Not particularly great, but unlike throwing axes and daggers, it has respectable range. It is a hammer though.

Bracers of Icelandic Pearl - Horrid Wilting can be useful against enemies with evasion (Viper Fang assassins in chapter 5 come to mind).

If anybody needs a refresher, here's itemlist for IWD2> http://www.weidu.org/IWD2-ItemList.txt