Melissa gave me the neatest book for Christmas this year, all about making books by Esther K. Smith (you should go get this book!). Inside there is a very simple way of making a little book from one piece of paper that I have been experimenting with obsessively. They are infinitely handy, these books - you can quickly whip one out for your kids to draw or write in, use them for little birthday cards, or as invitations. Yes, the possibilities are endless! The best part, as the author points out, is that the books are very easily reproduce-able. When unfolded, all the text/design is on one side of the page. So you can photocopy as many copies as you like and then fold them right up.
In case the pictures are not clear enough on their own, the way you make one is by folding a piece of normal notebook-size or copier paper in half the short way, and then in half lengthwise. Then you take it and fold it again, so that you have 8 little folded rectangles. Unfold it all, then fold it again the short way, and cut the middle fold (see the photo). Pull it back open. You should be able to see at this point how it folds together into a book. It's magical, and very easy once you start playing around. Have fun folding!