Today's letter is A, and an obvious choice of item is April Fools' Day.
A coworker's comment sums up my attitude fairly well: "I hate April Fool's Day and St. Patrick's Day with equal vigor and for the same reason: both encourage amateur hour bumbling in areas I consider myself a semi-pro."
Except I'm not a semi-pro at either, but most of the April Fools' pranks out there really feel like amateur night. (As it has been said, Sturgeon was an optimist.) Even Google's famous ones haven't thrilled me much recently, although YouTube has generally done well. It's hard to top Rickrolling everyone, though.
That said, there have been some good ones. Thinkgeek usually has some impressive products lined up for the day (favorite for today: plush bonsai kitties).
I think my favorite for sheer effort so far is Scalzi's The Shadow War of the Night Dragons Book One: The Dead City. It's hard work to write that badly.