The American Dialect Society has voted "Truthiness" as the word of the year 2005. It means "the quality of stating concepts or facts one wishes or believes to be true, rather than concepts or facts known to be true."
Other winning words include:
muffin top: "the bulge of flesh hanging over the top of low-rider jeans" (we call those "love handles" in Britain).
whale tail: "the visible appearance of thong or g-string above the waistband".