I was just getting out our Father's Day gift for Aaron, and thought I'd share.
It's not a surprise, really, it's something that we add to every year. The idea came from Family Fun magazine a few years ago. Instead of having the kids make cards every year (and then losing them, throwing them away, or (worse of all) finding space for them somewhere) we have a Father's Day book.
Just a nice hardcover spiral notebook. I've yet to do anything creative to the cover... I'm no scrapbooker.
Inside I put a recent group shot of the kids, the year, and then each kid gets their own spread (2 pages) to do what they want. 
(by Princess - 2005 - her in the purple wading pool)
I write the year and their current age at the bottom of the pages, and I try to include a hand print each year.
As they get older, the kids will be able to write stories or letters to their Dad in this book, and I hope it stays a special thing.
This is only our 3rd year of the book, but it's already fun to flip through and see how much everyone's changed. 
I think I like it more than Aaron...