Frozen Orb

This item drops from end bosses in Wrath of the Lich King instances on heroic mode.

As a currency
This item can also be bought from the following vendors for :

Frozo the Renowned sells various items in exchange for Frozen Orbs.

Notably:

Blacksmithing

 * Brilliant Titansteel Helm
 * Brilliant Titansteel Treads
 * Spiked Titansteel Helm
 * Spiked Titansteel Treads
 * Tempered Titansteel Helm
 * Tempered Titansteel Treads
 * Titansteel Bonecrusher
 * Titansteel Destroyer
 * Titansteel Guardian
 * Titansteel Shanker
 * Titansteel Shield Wall

Engineering

 * Armor Plated Combat Shotgun
 * Armored Titanium Goggles
 * Charged Titanium Specs
 * Electroflux Sight Enhancers
 * Greensight Gogs
 * Nesingwary 4000
 * Truesight Ice Blinders
 * Visage Liquification Goggles
 * Weakness Spectralizers

Inscription

 * Faces of Doom
 * Iron-Bound Tome

Jewelcrafting

 * Icy Prism
 * Titanium Earthguard Chain
 * Titanium Earthguard Ring
 * Titanium Frostguard Ring
 * Titanium Impact Band
 * Titanium Impact Choker
 * Titanium Spellshock Necklace
 * Titanium Spellshock Ring

Leatherworking

 * Durable Nerubhide Cape
 * Earthgiving Boots
 * Earthgiving Legguards
 * Giantmaim Bracers
 * Giantmaim Legguards
 * Ice Striker's Cloak
 * Icy Scale Belt
 * Icy Scale Boots
 * Icy Scale Chestguard
 * Polar Boots
 * Polar Cord
 * Polar Vest
 * Revenant's Breastplate
 * Revenant's Treads
 * Trollwoven Girdle
 * Trollwoven Spaulders
 * Icescale Leg Armor

Tailoring

 * Brilliant Spellthread
 * Deathchill Cloak
 * Ebonweave Gloves
 * Ebonweave Robe
 * Frosty Flying Carpet
 * Glacial Robe
 * Glacial Slippers
 * Glacial Waistband
 * Moonshroud Gloves
 * Moonshroud Robe
 * Sapphire Spellthread
 * Spellweave Gloves
 * Spellweave Robe
 * Wispcloak