For kids, I love to give funny books. Some of my top picks for funny gift books are:
Stuck by Oliver Jeffers: full of wonderful absurdity. We never get sick of it.
Bully by Laura Vaccaro Seeger: unexpectedly funny, with a point.
That Is Not a Good Idea! by Mo Willems: hilarious twist ending and lots of kid participation.
Also, you can never go wrong with my very favorite picture book, Extra Yarn by Mac Barnett.
Or Red Cat, Blue Cat by Jenni Desmond.
I'll force myself to stop there, I could go on forever. If you're interested in more ideas, check out my Best Picture Books of 2013 or 31 Days of Children's Book Crushes. If you have a Young Adult you are buying for, check out 31 Days of Young Adult Book Reviews for ideas.