A big vote for the Passporter. In addition to being a reference manual, the trip planning folders allows you to have everything in a single book, including hotel and air reservation numbers, priority seatings, things you want to see and do on a given day (so you don't forget), and space on the same-day pages to write down things to help you remember the trip, such as the weather, the best thing that happened that day, etc, and something we found VERY helpful in the past, which is reminders on what you want to do next time.
We use a pile of manuals, and I haven't seen a bad one yet (although see tjkraz's comment on Birbaum's and take their info with a grain of salt, it's half information, half Disney commercial). We cull information from each. Then we map our strategy in the Passporter and wouldn't be caught dead in the park without it.
Ok, if I left it at home I wouldn't cancel the trip! But it's a big help.
pat