The Rasterbator lets you create huge posters by breaking images down into smaller chunks that your printer can handle. All you have to do is upload an image, chose how big you want to make it, print out the pdf. file, and assemble everything on your wall. You may have to splurge a little on paper and ink cartridges, but otherwise, Rasterbating is free.
How large can you go? The site says 20 meters, but some images in their gallery show that you can go much larger.
So what are you waiting for? Turn your little 4 x 6 inch print into a 4 x 6 meter mural.
(Image via Rasterbator gallery)