There are tons of ways to make your own pinhole camera out of everything from a juice box to a pine nut. If you have a DSLR, you can make a DIY pinhole lens for it for just a few bucks. David O'Sullivan over on DIY Photography made this one using a cheap body cap and an aluminum can. Here's how to make your own.
David put up a template you can follow to make things easier, so start off by downloading it, then use a ruler to draw a line directly through the center of the body cap. Cut out the template and place it on top of the body cap, making dots where the holes will go.
Drill the holes using a 3mm drill bit, then use a 6mm bit to make them larger. Now, cut a square from the aluminum can and use your template again to cut it into a circle the same size as the body cap. Mark the spots on the aluminum just like you did on the cap, then use the pin to drill small holes, removing any burrs with sandpaper.
Align the holes in the aluminum with the ones on the body cap and glue or tape them together. Finally, use small pieces of tape to create a "shutter" for each hole.
Here are a few shots David took with his.