I've been meaning to thank you for this terrific list: you've definitely given us some great ideas for nieces and nephews this year!
Depending on the age of the target audience (trending a little older than your top 10), I'd recommend all those magnificent Martin Gardner collections (now available in one big CD-ROM for not too much money), and in a more modern version, the various books by Ian Stewart, especially his older stuff like "Game, Set, and Math" for instance.Also Raymond Smullyan, like "What Is the name of This Book?", though those are a bit more logic than mathematics. "Satan, Cantor, and Infinity" gets a bit more toward math.Honsberger's Mathematical Gems books are also pretty fun.Peter Winkler ... Ravi Vakil's "Mathematical Mosaic" ... I could go on for a long time. I'm glad I didn't have to narrow it down to a top 10.
I like most of those too, but think they feel the same way short stories do to me, a bit too scattered. In fiction, I like novels better, and with math I like books with more of a storyline, like Euclid In the Rainforest and (can't believe I left it off the list) Math Girls..