Spellfire Bag

Source
This item can be crafted using Tailoring (375); taught by.

Remember, the crafting has 4 days cooldown, so creating this bag can be quite long (and buying quite expensive). However, if you have the spellfire specialization, you can craft 2 from 1 casting.

Note: As of Patch 3.0.8 there is no longer a cooldown on Spellcloth.