Last year when we went, we tried to keep the destination a secret as long as possible. We were driving from Chicago, and I bought a big wall map of the United States I made up a few clues for each large city/landmark we would be passing through, and pictures representing each fun activity we would be doing either on the way, while we were there, and on the way back since we had tons of things planned outside of Disney, too.
About 3 weeks before the trip, I read one set of clues to the kids per day (6th, 2nd, and Kindergarten at the time, and obviously the 6th grader helped the little ones out!) and they had to figure out what city/landmark the clue was about. Then they marked it on the map, where they soon had a line going from Chicago to Florida and back. On the days where we reached a spot where we had an activity planned for that location, I would show them the picture, and they could guess what the activity was as well.
Once they knew we were obviously going to Florida, I started to show them the pictures of the resort hotel we were staying at (Hilton Convention Center on I-Drive&the BEST pool area for kids I have ever seen in my LIFE!!!), and the rest of the things we would be doing - Atlanta Falcons Stadium tour, Mammoth Caves, Cocoa Beach, I-FLY Indoor Skydiving, Gatorland Zip-lining, Disney, A Detroit Tigers Spring Training game (we are originally from Michigan!), etc. The kids LOVED getting their clue in the morning, and got more and more excited each day. It was really awesome.
This year, we are going to DW only and staying at POR, and the kids have NO idea we are even taking a trip. I will pack everything in secret and leave the bags hidden in my closet. We leave on a Thursday in November, and DH and I are planning on waking them up as if it is a normal school day. We are counting this as part of their Christmas gifts (now they are in 8th, 4th, and 2nd grades), and have been BEGGING us to go back, but to fly down this time, even to the point where they have all said that they would rather have a trip for a gift than toys (no worries - we are still getting them a few things for Christmas! LOL).
We are going to get their Christmas Stockings and some lights/small decorations out when they go to bed the night before, and I will put their plane tickets, their magic bands (if we get them!) or their KTTW tickets, a $50 Disney gift card per kid, a pair of sunglasses, sunscreen, and a new bathing suit each into their stockings, along with a portion of a progressive note that each will take a turn reading that will say something along the lines of "Santa heard your request, and he came early to three very special kids to bring you the trip you have asked for - get dressed and ready to go - our flight leaves in four hours -we are going to Disney World!!!!" I have not shown them the DW planning DVD yet because I am afraid they will figure out that we are going, so I thought that I would put that in and play it as they are waking up J
Hopefully they will be super-excited LOL and after we get dressed, we will be ready to head to the airport!!!