Press Here lately and I've added it to my wishlist, so when I saw The Game of Light in my local(-ish) Waterstone's I pounced on it.
It's a small board book with each page featuring cut-out shapes through which you shine a torch to project the shapes onto the walls and ceiling.
We rushed home and grabbed the only torch we could find - a dinosaur torch that roars when its mouth opens to reveal the torch itself. It didn't work brilliantly with the book - the dinosaur's mouth kept getting in the way - but 2-year-old Joe was transfixed as was 7-year-old Harry when he got home from school.
Such a simple, but brilliant, idea. I'll be buying copies as gifts for all the children I know.