Fuji makes instant pack film (3.25 × 4.25" images), which is fun and cheap. You'll need a Polaroid 405 holder, or the Fuji PA-145 holder. The color material is FP-100C, and the B&W is FP-3000B. Unfortunately, The Impossible Project was not able to save Polaroid's 45 or pack film machines, so they will probably not be offering a 4×5 material in the near future. However, a man named Bob Crowley is working to bring an improved version of Type 55 to the market, with his New 55 Project.