All currency items
Top 4 (from reddit thread):
Exalted Orbs Enchants a rare item with a new random property. Right click this item then left click a rare item to apply it. Rare items can have up to six random properties.
Divine Orbs Randomises the numeric values of the random properties on an item. Right click this item then left click a magic, rare or unique item to apply it.
Chaos Orbs Reforges a rare item with new random properties. Right click this item then left click a rare item to apply it.
Gemcutters Prisms Improves the quality of a gem. Right click this item then left click a gem to apply it. The maximum quality is 20%.