Alice's Adventures in Wonderland by Lewis Carroll
I loved this book when I was little, and I still do - it is only today that I realise what an incredibly trippy book this is, with the implied drug references (a mushroom where one side makes you big and one side makes you small, for example). This book is full of weirdness, and has lots of funny moments - the Cheshire Cat, the Mad Hatter and the March Hare all make me smile every time, as does the bizarre poetry.
I remember watching Disney's version many times, but it always bothered me that they stuck in Tweedledum and Tweedledee and the talking flowers, who are characters from Through the Looking Glass; Disney also managed one of the most harrowing scenes I've ever seen in a kids' movie, when Alice ventures into the Tulgy Wood and encounters various animals that look like writing equipment, and then a dog with a brush for a face sweeps out the path and she ends up lost; it came close to traumatising me as a kid.
I love the fact that in the book, there are lots of jokes I actually got when I was older that went over my head as a kid, but I would love to know the answer to the question - "Why is a raven like a writing desk?"