When we were planning the wedding, one thing I was sure of was that I didn't want a traditional guest book. I knew that if there was just a book on a table, half the guests wouldn't sign it in the first place, and at the end of the day it would go in a box. I wanted something that we could display in our home.
So instead of a guest book, we had our guests sign either the matting of one of our framed engagement photos, or a big wooden W. We have both of them hanging up where we can read the sweet notes from our friends, and they look pretty good :)
If a guest book is the way you want to go, go for it! I have friends that made really cute ones on Shutterfly full of pictures of them and their friends that they display on shelves in their homes. But if you want to get more artsy with it, go with a picture, your initial, or even a painting that means something to you (that you don't mind having people write on, of course). Weddings are so personalized nowadays, you can really make your guestbook whatever you want!