If you got your first NXT kit over Xmas and you are reading this, consider ordering a copy. It has some excellent reviews already and well worth the $19.77 special from Amazon.com. Some of the larger books shops are starting to stock it in their shelves as well.
One of the coolest models in the book is the BobCat that can be built with a single NXT kit. The BobCat is pretty unique model and both the skid steer and the arm works really neatly and it is really nice to watch it in action.
My kids had great fun building the Bobcat from the Book. They adopted it to carry drinks from one part of the house to the other: