Mark Elsdon's Worker's Diary could well be the easiest, most direct and 100% self-working diary effect of all time!
In effect, a spectator is handed a diary. All the dates have playing cards written next to them. The spectator verifies that there is no pattern and the cards do not repeat on the same day each month. It is genuinely random. You display a blue-backed deck which, you tell the audience, contains one card from a red-backed deck. The spectator looks up their birthday and notes the card for that date. The day before and the day after - in fact the whole week - all have different cards written next to them. The same day in the previous month, and the month after, also have different cards. You remove the card that appears at their birthday and place it into their hand. There's only one thing left to say: "Happy Birthday!" The card is turned over. It has a red back with the words "Happy Birthday!" written in large bold, black letters!
Works with any date - you DO NOT need prior knowledge of the spectator's birthday!
Revealing personal information to a stranger is one of the strongest effects you can perform. The special deck included within does ALL the work, allowing you to concentrate on the presentation. With "The Worker's Diary", it appears that you personalized the entire effect, just for them.
The Worker's Diary really says it all! A super clean genuine miracle involving a spectator's own birthday that plays just as well for a room full of people as it does one on one.