w00t (pronounced "woot") has always been my favorite l33tspeak word of all. Supposedly, it started out on gaming message boards as an acronym of "We Owned the Other Team", and then was converted into l33tspeak by changing the o's to zeros.
Regardless of the actual origin, though, it's a wonderful interjection that just means "woo-hoo!" and is a great way to express delight on any occasion whatsoever. It also holds the distinction of being named "Word of the Year" for 2007 by Merriam-Webster Online. Who'd a thunk?