leafletdocument class. It automatically sets up a layout for 6 small pages on 2 normal-sized paper pages, so that you can print the output PDF out on double pages, then fold it up into a real, er, leaflet.
Here are the thumbnails of my leaflet, and here are the source code. Notice the little mark (highlighted by the red circle) on the second page to guide you in folding the leaflet. Just make sure that you set your PDF viewer to “Do not scale pages” when printing the PDF.