In the new Dungeons & Dragons 3rd Edition game:

Cloak of Elvenkind: This cloak of neutral gray cloth is indistinguishable from an ordinary cloth of the same color. However, when worn with the hood drawn up around the head, it gives the wearer a +10 circumstance bonus on Hide checks.
Caster Level: 3rd; Prerequisites: Craft Wonderous Item, invisibility, creator must be an elf; Market Price: 2,000gp; Weight: 1lb.

These are often used in conjunction with Boots of Elvenkind.

Update 9/16/2003: Ouroboros says re Cloak of Elvenkind: Would you take note of the 3.5E changes that set this to a +5 bonus?