The guestbook is your way to remember who was there to celebrate your special day with you. In the hustle and bustle of everything going on, someone may slip your mind. This is one way you can prevent that. Normally, the guest book is relatively boring. It is more of a chore that you are putting your guests through. Try doing something more exciting.
Instead of a book, have them sign a piece of art that you can display in your home. For example, you may want to have a painting of a tree, and each leaf is a place for a guest to sign their name and maybe leave a short note. You could do the same thing with clouds, stars, or anything that is important to you and your new spouse. This way will also encourage everyone to sign since they will feel as though they are contributing to a piece of art as opposed to putting their name in a book that will likely just get put in a box for many years.
To make it even more special, you can make the painting yourself or have someone close to you design it. It will be a beautiful reminder that you can adorn your home with as husband and wife.