There are so many!
I want to read Lisa Gorton's Cloudland because I just finished her latest poetry anthology Press Release and it was beautiful. I am part way through Richard Feynman's Six Easy Pieces and looking forward to some more time to sink into it.
The book I most want for Christmas is Denniston's The Greek Particles. This is a fairly obscure book and I have been trying to track down a copy for a few years!