The ones I remember are the next:
Life Crystal into Life Ring with Chester Kahs in Thais.
With the NPC A Sweaty Cyclops you can trade these Items by saying the word at the end:
Devil Helmet into Piece of Hell Steel (Za'Ralator)
Crown Armor into Piece of Royal Steel (Uth'Kean)
Dragon Shield into Piece of Draconian Steel (Uth'Lokr)
Giant Sword into Huge Chunk of Crude Iron (Uth'Prta)
Gear Wheel into Iron Ore (trade Iron Ores for Gear Wheels)
Gold Ingot into Cup of Molten Gold (item to tame White Deer)
Soul Orb into Infernal Bolts (3 bolts per orb)
In Venore city you can trade:
Mystic Turban into Blue Piece of Cloth (with NPC Irmana)
Red Robe into Red Piece of Cloth (with NPC Irmana)
150 Green Tunics into 1 Green Piece of Cloth (with NPC Irmana)
In Adventurer's Guild you can trade:
You can exchange Gold Tokens with Yana for Creature Products or Weapons.
Or Silver Tokens for Addons with the same NPC.
You can also trade 20 Silver Raid Token for one Replica of any Fansite Item with NPC Jorge.