The Icy Dragon Sword (commonly abbreviated to "IDS"), like its cousin the Fiery Dragon Sword, is a popular sword that is prized for its style. It has a unique look, with its frosty blade (only two twisted "filaments" as a solid core) coming out of the dragon's mouth that acts as the hilt.
The only alternative is to buy the sword from a fellow player. To purchase this sword, the easiest place to find it on sale is in the Granite Citadel, which is the starting point for IDS farming runs.
Applying dye to an Icy Dragon Sword affects the hilt. Dyes cannot change the color of the flame.
Icy Dragon Swords were added to the game on December 20th, 2005. They seem to be an undocumented addition ("hidden Christmas present") by ANet.
These swords are available year-round. They were believed to be only available during the Wintersday 2005 update, but have since been confirmed by Gaile Gray to be available all year. According to her it is "a new weapon for a new year".