I used a 5x7 album for my kids' autographs. However, I had read that predecorating the pages can lead to problems. For example, the character accidentally (or on purpose - in the case of some of the villans) signs the wrong page, signs the book upside down, etc. Or you may not get all the characters you made pages for and then what happens to the empty page.
However, I wanted to predecorate my pages.

I used scrapbook stickers. if you go to Michaels or AC Moore you will find oodles of Disney stickers to choose from. To avoid the "holding up the line while I flip through the book to find the right page" problem, I used cardstock. (pieces of scrapbook paper cut into 4x5 rectangles). You could buy this pre-cut or make your own. I carried these predecorated cards in alphabetical order in a coupon organizer. I also had blanks for characters we weren't expecting. We were able to quickly find the right card and present it to the character to sign. We also brought a small clipboard to put the card on. We used Scrapbook markers with the fat tips to make it easier for the characters to hold. This had the added benefit of not having to lug around the whole book everyday, we took the signed cards out every night, so if we lost it we only lost one day's worth of autographs, and it was protected from the rain.
When we got home we put the autographs in the album and put a pic of DD with that character on the opposite page. We decorated the pages even more. The girls had so much fun doing this. Also, the characters had fun reactions when they saw their predecorated cards. Eeyore was especially thrilled and Mulan wondered where I found stickers of her.
Whatever you do, don't worry so much about being "creative" just do something fun. It will be special because you made it
Laurie
ps -you may get more responses on the scrapbooking board
