Drake Scales are a rare item dropped by the Drake family of monsters located in the Mountainside Caverns while doing the quest The Urn of Sacred Ashes. There is a finite number of scales to be found (up to seven on the PC version, 10 on the console versions), which can be traded in for two sets of armor at Wade's Emporium. A seventh Drake Scale can be obtained by agreeing to help Kolgrim, and then killing him once he speaks to the High Dragon.
Aside from Wade's Drake Scale Armor sets there are no known uses for Drake Scales.
Use
Drake Scales can be given to Wade in Wade's Emporium in Denerim to receive a set of Wade's Drakeskin Armor and Wade's Superior Drakeskin Armor.
Note
In Dragon Age: Origins - Awakening, two drake scales can be obtained in Silverite Mine.(Drake scales have no use in Awakening so it is safe to sell them.)
There are some reports of drakes and drake scales in other parts of the game such as the Deep Roads and Elvish Ruins. Whether this is incorrect, or a random enemy/drop scenario, or a glitch from un-updated versions of the game is unknown.