I just surprised my kids with a WDW trip this August (even though we had just gone with my parents in March, it was just too good of a deal for a Dis'er to pass up).
I told them that I was taking some time off and on Thursday we were going to get up early and go to Chicago (all factual info, but they were thinking like zoo, museum, Sears Tower...etc). We they woke up that morning I said I had a game for them to play. I had printed up cartoon pics on the computer to give clues to spell out "How Would You Like to go to the Happiest Place on Earth...TODAY!"
(example - the phrase "question word that rhymes with..." and a picture of a cow = how)
Even though it was like 3:30 am when they were doing this, they figured it out and the "TODAY" one was just the word with a Mickey sticker. They were a bit confused still and asked me "when?" I pointed to the sign and said "TODAY! Cab will be here in an hour go get ready to go".
They were soooo shocked, my DD7 laid out flat on the floor as if she had fainted and my DS11 still can't figure out how I kept it a secret. I was so excited the night before I almost threw up LOL.