[kokofoo]

If you want to boggle your mind this Christmas I suggest you read GEB. It's not just Math, but Philosophy, AI, programming, logic, human mind, etc. I started reading it last year, and I'm still reading it this year, probably will be next year, year...

[cabalamat]

I second this recommendation, though I suspect most people at HN have already read it. I can also recommend two other books by Hofstadter: Metamagical Themas, and Fluid Concepts and Creative Analogies