My wife got me this year. She waited until I was half asleep and she was rubbing my back. She casually slipped in something like, "by the way, I bought $300 worth of lottery tickets." I woke up pretty quick and she started laughing and reminded me of the day.
A couple of years ago was more fun. I went in on it with a co-worker and we went after many in the office and a few mutual friends. Pranks included the timeless "Mr. Lyon called while you were away" (Number to the zoo)...We left "love notes" two two co-workers inboxes trying to get them to meet. They worked at different times of the day and it half worked on one, but the other one knew right away.
The best though was a mutual friend. She was from Canada and going to grad school at the time. I didn't know her that well, so she didn't know my voice. My co-worker game me lots of info about some school department that was sponsoring her visa (or something like that). I called and left a message saying that I was calling from that department and that someone from the FBI wanted to talk to her ASAP about her associations with a made-up Arab-sounding name. I went on-and-on in the message. At the end I handed the phone over to the co-worker who screamed "April fools, gocha!" or something.
I was fortunate enough to be there when the co-worker got called back. I guess the friend completely fell for it.