Core Mac OS X and Unix Programming
Currently reading/browsing this book. Its pretty interesting and goes into a lot of detail on lowish level unix stuff.
Has a great section on gdb (the debugger) as well, amazing what you can do with that if you know the right commands.
hrmmm, other books im reading in some shape or form include:
* Applescript the definitive guide
* Numbers XLib and X11 programming books
Thats about it. I havnt read a non computer related book in a while. Seems to be something i dont do much anymore. *shrugs*