Corrupted Crystals let you corrupt Rings, Amulets, Magic, Rare, Set, Unique and Crafted items (sacred only):
Corrupted Crystal + Item --> Returns Item with a chance of adding bonuses, a chance of doing nothing, and a chance of making the item unusable.
Since there doesn't seem to be Official Documentation on Corruption Crystal outcomes, this thread shall hereby serve as the Unofficial source.
All possible bonuses are applicable to any given item. They are not specific to any particular item class.
List of Possible Corruption Bonuses:
+1 to All Skills
+1 to Maximum Elemental Resistances
+1% Fire/Lightning/Cold Absorb
+3 Light Radius
5% Deadly Strike
10% To All Attributes
15% Poison Length Reduction
20% Attack Speed
20% Block Speed
20% Faster Cast Rate
20% Faster Hit Recovery
20% Gold Find
20% Movement Speed
+25% Magic Find
+30 to (Strength or Dexterity or Energy or Vitality)
10% Spell Damage
10% (Fire or Light or Cold or Poison or Phys/Mag) Spell Damage
-10 Enemy (Fire or Light or Cold or Poison) Resistance
15% (Fire or Light or Cold or Poison) Resistance
+60 Spell Focus
+100 Life
+150 Mana
Physical Resist +4%
+15 to Maximum Damage
40% Enhanced Weapon Damage
+10 Life Regenerated per Second
-5% to All Vendor Prices
Regenerate Mana +10%
Slow Target 4%
Slows Attacker by 5%
+5% Life
+10% Mana
Item Becomes Ethereal
Requirements -20%
unique jewel and another normal one each time
and an umo 
