The Signing Board, popular at Bar and Bat Mitzvahs, is a great idea for any event.
A Signing Board is an enlarged photo mounted on foam board that is displayed on an easel at a party. Guests autograph the board using permanent markers by writing a little message for the guest of honor and signing their name.
The easiest way to make a Signing Board is to have a pro do it, such as Kinkos or a similar copy center.
These boards are typically 24" x 36" and provide a wonderful activity for guests and memory for the guest of honor.
Another way to go is to purchase a large autograph board, available at many party stores, and to put an 8" X 10" photo in the center. Guests can autograph around the photo.
You can also make a big photo poster by using an all-in-one copier such as the HP Photosmart. Many of these high-end copiers have a "poster" option where you can enlarge a photo that prints on to many sheets of paper. Then, you assemble the paper, like a puzzle, to create the photo and then tape or glue-stick it on to a large piece of foam board or cardboard.