One thing we have heard about a lot is the Disney trip surprise. I have always wanted to try it so we thought we would give it a shot this year. Luckily our kids are young enough that they are pretty oblivious to the conversations we have and don't have very good short term memory anyway.
We left midweek but due to a last minute illness we were not able to pack until the morning of our trip. We let the kids watch TV while we ran around and gathered up princess dresses and dragon costumes from various corners of the house. Finally, I dressed them up in Minnie and Mickey garb and turned on the video camera. At this point they still had no idea. Ha!