If you haven't made a purchase yet, keep an eye out on Cameta Camera - very reliable Internet retailer with a lot of access to Nikon refurb units, including the D3100. Coincidentally, they're in the same area of NY as Nikon USA HQ, which may go a ways to explain their access to a lot of such kits. They also have many sales via Amazon and eBay, but buying direct from them is just as fine. That's where I picked up my D3100 kit. Free shipping can't be beat.
Also, for the back of the camera, one of the best investments I made is the Giottos LCD protector. Made of Schott glass from Germany, fabulous transparency factor and extremely durable. You will never lose it because it adheres to the sides of the camera around the LCD screen.