Wasabi is a variety of green horseradish, the powder has a sharp flavor that's a bit hotter than the familiar white horseradish.

Wasabi powder provides a nice change of pace from chiles. It provides heat, but has more of an herbal overtone and dissapates more quickly. You can also use it as a substitute for Dijon mustard, or as a flavoring in home-made mustards.
Combine equal parts of wasabi powder and warm water to make wababi paste, similar to the familiar sushi accompaniment. You can also make an easy wasabi cream sauce in the same manner, just add warm cream until you reach the desired consistency.

Wasabi is a great compliment to almost any asian dish. Try adding a dollop to you mashed potatoes, or mix it in with some mayo for a sandwich.