I used to carry around, what I called my "Bible." It wa a small zippered book with a notepad, places for credit cards, PDA, and such. It was great for lugging around maps, tickets, take notes, etc, etc.
Then, I found the Passporter. This is the best thing since sliced bread for my fellow organized (somewhat anal-retentive) Disney vacationers. I happened across it at a Barnes & Noble, but I think they mainly sell them online. I HIGHLY recommend it.
It's about $20-25, and it has EVERYTHING you need to stay organized at the parks. EVERYTHING. Maps, suggestions, itineraries, PS reservations, notes, autographs, budgets, pouches to hold things... you name it. Plus, it has reviews and suggestions for every WDW resort and restaurant. I bought mine about 2 years ago (the 2004 edition). They post free "updates" on their website for download into the book from time to time. We've used it about 7 times since then. It's getting a little war-beaten, but it's still a valuable resource.
It's the same size as a small book, easy to carry (or throw in a backpack). And, another nice benefit, a large amount of the CM's that noticed it, started up a conversation with me. Apparently, they're very aware of it and it's pretty well known. Those conversations, at the least made a new friend. In many cases, the conversations led to some CM "tips" on how to do the parks that day (when to hit what rides, etc.).
I can definately see that there was a LOT of time and effort into putting this book together. It is very organized, very well thought out, very detail oriented - from the flaps which were designed so you don't lose your place, to the strap that holds everything together, to the stickers to help personalize/customize your book.
It's a small investment with a great return.