The first time I put a card in her cereal box the morning of the trip. When she poured the cereal, the card poured out into her bowl and after the shock and happy screaming we jumped in the car with the already-packed suitcases to catch the plane.
Second time, I created a fake mailing label addressed to her, put the most recent Disney guidebook in a box with the label and when she got home from school I told her to go get the mail. When she opened her package, I told her that I had ordered her a book because she needed to practice her reading and I wanted to bring her some Disney Magic. Previously, on the Pop Century description page I had stuck a post-it that said "We're going here very soon!! Find the clues in the book to know when." I had circled the page numbers of the book that made up the month and day of our trip. It was hard to wait for her to read all the way to the post-it but I knew she would get there eventually. One night a few days later I heard a big scream coming from her room and knew she had seen it. That second time was even sweeter than the first time because we had time to plan everything about the trip together.
For this upcoming trip...I asked what she wanted to do for her birthday and she said, "I wish we could go to Disney World..." She had been mooning over the most recent Disney commercials on TV and taking out the scrapbooks, so I already had bought tickets and was waiting for a good time to bring them out. I told her later that night to go get me a pair of socks because my feet were cold. When she opened my drawer, the tickets were right there.
I think I enjoy this even more than she does! Whatever way you choose to reveal the news, it will be special and always remembered.