Something else to consider is Hori band screen protectors. Chanced across some of these in Target one day. They're a very good protector, though the instructions for applying them aren't so great. The english translation leaves something to be desired, but then again, it's not really all that difficult to work out.
Thing I liked about the Hori protectors, is they don't require a special water based solution to be sprayed on them like Invisible Shield does. They can just be hard to come by outside of Asia. You might want to opt NOT to install the full body protection if you have any color DS Lite than white. The protector will be clearly visible then, but the screen protectors are very good. Unless you really look hard, you cannot see them once applied. So no visual quality loss like some screen protectors introduce.