Yay! A day to celebrate all things bookish.
Actually I think this is aimed more at children than surly middle-aged librarians, so here is one of my all-time favourite children's books.
The Stinky Cheese Man by Jon Scieszka.

On World Book Day you are meant to come to school (or work, presumably) dressed as your favourite literary character. In case you are wondering, I'm not sitting here dressed as Stinky Cheese Man.
Err, I really hope I'm not. But anyway, it's a ripping yarn and you learn stufff like this:

I think there's a message there for all of us.
Currently I am reading Mirrors by Eduardo Galeano.

As the title suggests, it is a history of nearly everyone and everything, and it's written in handy bite-sized chunks so you can read it on the tram without being distracted completely by other people's phone conversations. It's a cracking read and, again, one where you learn stuff. Like Hitler's troops were dressed by Hugo Boss, and Fanta was invented for Nazi Germany because they were having trouble getting Coca Cola into the country.
I've always known that Fanta is a reprehensible beverage.