Do you need an infinite amount of Frostweave Cloth? Do you have a high-level character with a AoE attack? Yes? You're in business!
Teleport to Dalaran, then fly north to Icecrown at 70,61. Land at that spot and begin AoEing! You want the Vicious Geists, as they carry the Frostweave. If you can tag a couple vicious geists on the periphery and get them to come to you without your moving, so much the better!
Stand in one place and the geists will come to you! It's like pressing a button and having Frostweave Cloth just tumble into your bags.
Using this method, one may acquire a stack of Frostweave Cloth in five minutes, I kid you not. Or three in 15 minutes!